Modus tollens tollendus est ! (iterum re-updated anew)

In philosophy there are very few  and perhaps no valid  logical-impossibility  or reductio ad absurdum  proofs.

-- Alasdair MacIntyre, After Virtue (1981; ²1984), p.  101

Wer A sagt, muss auch B sagen.

-- old folk-saying

Die bürgerliche Stellung des Widerspruchs

-- L. Wittgenstein, Philosophische Untersuchungen, #125

An example of epistemological ‘character armor’:

All scientific research programmes may be characterized by their ‘hard core’.  The negative heuristic of the programme  forbids us to direct the modus tollens at this ‘hard core’.  Instead, we must use our ingenuity to articulate or even invent ‘auxiliary hypotheses’, which form a protective belt around this core, and we must redirect the modus tollens  to these.

-- Imre Lakatos, “Morphology of Scientific Research Programs”, in I. Lakatos & A. Musgrave, eds., Criticism and the Growth of Knowledge (1970), p. 133

In political or religious ideology, there are obvious analogues of this ‘hard core’.  (E.g. 'sacred cows'.)

~

[This exercise originally began as a simple application of cool, unruffled logic  to a sociopolitical topic too hot to handle in less rarified terms.  The point was, If you were logically consistent, you would … (taceo).  But a working-out of the general intellectual idea  led, inevitably, towards that domain (mathematics, logic itself) where the very idea of consistency is most at home;  and led, less obviously, to a kind of backhanded defence of inconsistency  (wherein we follow our countryman Emerson, in his depreciation of that ‘hobgoblin of little minds’).

Modus tollens is that figure whereby, when a proposition entails a falsehood, that proposition is infirmed.   The procedure finds general acceptance among the logically inclined.  This essay considers cases where otherwise logical people nonetheless kick against the pricks of this restriction.

We now return to the original plan.]

~      ~      ~

It should be obvious that the fundamental objections to racism and sexism … apply equally to speciesism.

-- Peter Singer,  Animal Liberation (1975), p. 6; quoted in Stephen Schwartz, A Brief History of Analytic Philosophy (2012), p. 282.

Singer’s proposition has the form  “P => Q”;  we shall call it the “Singer Sentence”.  It is, so presented, a proposition, and no mere proposal, since he claims that it is “obvious”, presumably because founded upon a generally-accepted principle:  basically, What’s sauce for the goose  is sauce for the gander.    Since that principle is reasonable (we have often invoked it ourselves), though extra-logical, we have no a-priori quarrel with the Singer Sentence at all.

Suppose, however, that you yourself eat meat, wear wool and leather, and are content that rabid dogs should be shot.  Suppose further that -- selfish cad that you are -- you do not, like the saintly naked Jainist, wear a veil before your lips when drinking tea, lest you accidentally imbibe some supernatant insect.   Nor (for shame!)  do you enjoin your dentist and your physician  to refrain from administering anaesthia or antibiotics, on the grounds that these, having been developed with the aid of experiments on helpless animals, are fruit from a poisoned tree.   And suppose that (blast your impudence!)  you do not intend to amend your ways.  Well then, in effect, objectively, you hold that “not-Q”.  What follows from this?

What follows (by the most elementary logic -- the rule known as modus tollens) is that, if you assert the Singer Sentence, then you must needs conclude:  not-P.   -- That, of course, would be a political catastrophe.

Short of adopting Jainism, there are only a few ways out:

(1) Have recourse to a kind of meta-tollentic principle, to the effect that any set of propositions which entail not-P  must itself be denied, P being unantastbar.

(2)  Proclaim the truth of Q, even while continuing your carnivorous habits;  shrug apologetically; reference Emerson re the "hobgoblin of little minds".

(3) Boldly hold the joint and several validity of :
P;  P=>Q; and not-Q. 
Then utter not another word upon the subject.

Such a mindset is known as “doublethink”.  It is not so bad once you get used to it, judging by its millions of satisfied customers.

Cf:

Whether the ethic of ‘speciesism’, to use Richard Ryder’s term, can be put on a logical footing  any more sound that that of ‘racism’, I do not know.

-- Richard Dawkins, The Selfish Gene (1976; 2^nd edn. 1989), p. 10

(That ‘any more’ sounds rather half-hearted …)

~

There is a different sort of logic-chopping that may be operative in a case like this.   Someone wishes, for non-logical reasons, to assert that Q; then trumps up (fallacious) reasons for asserting that P => Q.   (Thus, currently, in a certain political fringe, the desired outcome is “It’s all Obama’s fault”.  Whatever P may arise in the world, a hasty P => Q is asserted, to reach the desired conclusion.)   But, for psychological and political reasons, I do not believe that Singer himself is here guilty of this:  he in all likelihood does feel ethico-logically compelled to deduce Q, however unwelcome that conclusion may be in many quarters.   For he likewise (by different steps) reaches a quite distinct and socially unmentionable conclusion (this time concerning deformed fetuses or the disabled), and one which is precisely of a nature to enrage that segment of society which would embrace his earlier conclusion about animals.  So, no, Singer was not trying to win any popularity contests.

[Footnote] For those of you in the quandary (2), here is the place 4 U to shop (courtesy of Garrison Keillor):

People’s Meats

Most of us accept strict vegetarianism as the best way,  but many find it difficult to change their eating habits.  People’s Meats is an interim solution.  All of our meat comes from animals who were unable to care for themselves any longer.  Hoping to phase out the operation, we do not advertise hours, prices, or location.  We do not deliver.

~            ~            ~

The analysis above was clad in sociopolitical raiment;  but its skeleton is logical, which is subject-matter-neutral.  Consider the following (which is skeletally somewhat distinct, but in ways  unimportant  for our purpose):

Let P be standard mathematical praxis.   (And here -- as seldom -- we actually are referring to the human practice of mathematizing, rather than to the timeless and species-independent truths of mathematics itself, whatever these may be.   For more on the distinction, see here: http://worldofdrjustice.blogspot.com/2012/08/on-nature-of-mathematical-knowledge.html.)

Something similar to the  P => Q step was broached about a century ago; it concludes (while using reasonable background metamathematical assumptions comparable to the “what’s sauce for the goose is sauce for the gander” enthymeme above) that this standard practice leads to paradox.  As John von Neumann put it,

A closer study of the merita of the case, undertaken by Russell and Weyl, and concluded by Brouwer, showed that the way in which  not only set theory  but also most of modern mathematics  used the concepts of ‘general validity’ and of ‘existence’  was philosophically objectionable.

-- quoted in James R. Newman, ed. World of Mathematics (1956), p. 2058

Must we then give up P?   Brouwer (a Dutch mathematician who had previously proved important results) now plays the role of Singer, and went on to his logical conclusion:

A system of mathematics which was free of these undesirable traits, “intuitionism”, was developed by Brouwer.  In this system  the difficulties and contradiction of set theory  did not arise.  However, a good fifty per cent of modern mathematics, in its most vital -- and up to then unquestioned -- parts, especially in analysis, were also affected by this “purge”:  they either became invalid, or had to be justified by very complicated subsidiary considerations.

-- id.

(That final clause is a far more dreadful consequence than might be apparent to those outside mathematics, since mathematicians prize elegance and generality of proof. )

Du muss dein Leben aendern ...

So -- shall we bow to these strictures, and surrender our mathematical meat? 

Von Neumann goes on:

Only very few mathematicians were willing to accept the new, exigent standards for their own daily use.  Very many admitted that Weyl and Brouwer were prima facie right, but they themselves continue to trespass, that is, to do their own mathematics in the old, “easy” fashion -- probably in the hope that somebody else, at some other time, might find the answer to the intuitionistic critique and thereby justify them a posteriori.

In short, the bulk of mathematicians adopted strategy (3) above.

Brouwer, like Singer, went on to make a pest of himself for many years.  

[Footnote]

Intuitionism -- initially a sort of mathematical vegetarianism -- is by no means dead.  Michael Dummet, no crank, espouses intuitionistic logic (I am currently painfully working my way through his essay on the subject, line by line.)   And it has subsequently morphed in ways that are quite beyond me, e.g. in topos theory.

[Footnote 2, a half hour later]  In his essay “The Philosophical Basis of Intuitionistic Logic” (1973), Michael Dummet writes (for our present purposes, the context is unimportant), concerning a proposal that he has just put forward:

What is involved is a thesis in the theory of meaning  of the highest possible level of generality.  Such a thesis is vulnerable in many places:  if it should prove that it cannot be coherently applied  to any one region of discourse,  to any one class of statements, then the thesis cannot be generally true,  and the general argument in favor of it  must be fallacious.  [dbj:  That last phrase has rather a Sherlockian cast to it.]  Construed in this way, therefore, a position in the philosophy of mathematics  will be capable of being undermined by considerations which have nothing directly to do with mathematics at all.

This amounts to offering a hostage to fortune -- specifically, a hostage to modus tollens, in its strong quantified form:    P => ∀x Q(x):  the existence of but a single exception (∃x  ¬Q(x) )  blows the whole game.

~

We need not have recourse to anything so rarified as ethics or metamathematics  to be confronted with an apparently (morally, intellectually) scandalous state of affairs:  It stares us in the face in that favorite tow-headed boy of the philosophy of science, physics.   And here, in that most venerable part of it,  Maxwell’s theory of electromagnetism.  Rock-solid in its own day, it survived (and even helped inspire) the introduction of Special Relativity.  It fit smoothly with the new developments in non-EM forces, graciously uniting with the Weak force to form the Electro-weak, and so forth.  And yet, in the context of the atomic theory, it was (if only in whispers) an intellectual scandal, since it predicted that atoms were unstable:  the whirling electrons would radiate energy away and quickly collapse into the nucleus.  Thus, the material world as we know it, could not exist.

Now, one stance of reaction in the face of so bald a challenge, is to say:  “R-r-right!  Science cannot err;  ergo, the world as we know it  does not exist.  Meta-ergo, we all are just brains in a vat.”   Such, in effect, is the path taken by contemporary eliminative materialists -- a shuffling tribe of hunchbacked ne’er-do-wells, who, faced with their irrefutable failure to derive free will, faith, thought, beauty, aspiration, or much of anything of value, from their prolonged and proctoscopic vivisections of sea-slugs and the like (to which the World of Dr Justice, friend to all creatures great and small, responds with the evisceration of eliminative materialists)  -- these gentlemen (stretching that word to its breaking-point), these … bipeds, conclude that Free Will is an illusion, faith and beliefs and reason  all one great gigantic joke, and that we are all just robots, brains marinating in a vat of simulation, or (barely) glorified sea-slugs.   (In this they are partly correct:  the eliminativists -- mark the name -- are but brains in a chamber-pot.)

So, are those who do not take that bold blind path, whenever some contradiction turns up, in a state of intellectual bad faith?

The answer is a subtle and qualified mmmm….n-n-no-o-o …..  For relief, we turn to Quine.

~

We frequently do turn to Quine for relief,  to savor his elegant pellucid prose, when the cacophony of the agora grows too rebarbative.    Yet it is not for his literary qualities that we seek him now, but for his (jointly with Pierre Duhem) holism.  Specifically, his celebrated doctrine that theses face the tribunal of experience, not single-spies, but as a corporate body.  There are (so to speak) concentric shells of propositions relatively dispensible and relatively central:  but in principle, none is immune to revision.  (Intuitionists have even gone dicking about with the Law of the Excluded Middle, and you don’t get more central than that. -- In that case, Quine was unimpressed:  “When you change the logic, you are only changing the subject.”  Rather a Platonist remark, that, Van.)

Thus, consider again the plight of electromagnetic theory, faced with the atomic paradox.  Its bacon was eventually saved, not by any refinement of that theory itself, but by an entirely unanticipated development:  quantum mechanics.

Now, there is no sense in which a pre-quantum physicist could have said “We saw that coming” or “Toleja so”.   Until the quantum theory arrived from nowhere, physicists had been content to simply live with the contradiction, in the classic fashion of Walt Whitman (“Do I contradict myself?  Very well then, I contradict myself.”)   And their quietism was justifiable, even during the years when no resolution was in sight.  For, Maxwell’s electromagnetic theory had done sterling service  both practically and theoretically, in a host of ways.  [This, I am aware, is intellectually comparable to the classic defense of Mussolini, that he made the trains run on time.]  The fact that it predicted an anomaly on the atomic level … well okay, an anomaly involving THE ENTIRE UNIVERSE BLOWING TO BITS -- but still, an atomic anomaly, not a macroscopic one (save secondarily), suggesting that one might, for the duration (until this beast be slain), simply wall-off the subatomic level (“there be dragons”) and get on with our lives.  It certainly did not make sense to throw out the Maxwellian baby with the anomalous bathwater.

In the case of EM, it turned out that there wasn’t even any bad bathwater to discard:  electromagnetism survived intact.   In the case of the aether, the anomaly was the Michelson-Morley experiment, whose results were later explained by yet another where-did-that-come-from new revolutionary theory, Special Relativity;  and in this case, the aether theory had to be discarded.   But both cases illustrate the thesis of Quine-Duhem, that when a body of doctrine is challenged, it is not initially evident which pieces must eventually give, and some may be close to the core of the structure.   In the case of Relativity and quantum theory, the transmogrification went deeply into the core indeed, upending our notions of space, time, causality, and continuity.   In retrospect, those curiously stable atoms seem not so bad;  the explanation is harder to live with than was the thing that was unexplained.

~

A word on our less-than-effusive approval of Quinean holism.

It is all too easy to imagine self-serving uses of such a principle.  As, Dennis the Menace, caught with his hand in the cookie-jar, exclaims:

“Mother, do not prejudge!  Granted, your B-fibres seem to present an image of someone resembling young Master Dennis with his arm hovering above a receptacle of some sort.  The hand itself -- which you suspect of larceny -- is not visible;  perhaps it has been tragically amputated, in which case the young fellow is more to be pitied than blamed.  Yet, how are we to reconcile this dubious alleged image with the far more desireable thesis that his character is pure as the driven snow?  Remember:  Propositions face the tribunal of experience as a corporate body!  Perhaps 'tis but an illusion of swamp-gas;  nay, perchance the fault lies somewhere in that oft-critiqued principle of Induction …”

(Later, as he sits with his pookie-bear in the familiar corner, he steams:  “But I had her epistemologically …”)

~

Of all human endeavors, surely mathematics is the most sensitive to refutations, however slight.    Yet behold this brawny scoffing attitude, specifically as regards the central and indispensible Calculus (famously the target of Bishop Berkeley’s barbs -- which it shrugged off):

If the calculus had not been ‘justified’ Weierstrass-style, it would have been ‘justified’ anyway.  The point is that the real justification of the calculus  is its success.

-- Hilary Putnam, “What is Mathematical Truth?”

Breezy, that!  Huey Long couldn’t have put it more pithily.

~

And now let us bring it all on home:  confronting the challenge of modus tollens, when a refutation or contradiction or paradox is met, in its home territory of mathematical Logic…

Celebratedly, the great German logician Frege  fell into despair (his masterwork already in galleys), upon being informed by Russell  of the latter’s eponymous Paradox. 

There we see  the logical conscience  at its most delicate.  For  Russell’s paradox, worthy though it be, is rather far-fetched, involving sets-that-are-members-or-not-members-of-themselves  (to which your average mathematician, let alone physicist, will say:  Huh??), all too reminiscent of the well-known but trifling Barber Paradox, involving a purported barber who “shaves everyone who does not shave himself”.  Paradox:  Does he shave himself???   Answer:  Fageddaboudit;  ain’t no such barber.

Rather other was the case of Quine’s Mathematical Logic.   In the version of its first edition (1940), this was shown to entail a contradiction.

Now:  an axiomatic system of logic, such as ML, is so tightly knit, that one bad apple really does spoil the whole barrel -- you can’t just shrug and say, “Nobody’s perfect.”  The situation in question, is generally held to be a catastrophe -- that any system which can derive a contradiction, can derive any proposition at all.

However, Hao Wang stepped in (ever the gentleman), and tidied things up, and all was well:  put right  in the second edition.

Haec fabula docet:  Contradictions are a bummer,  but don’t commit suicide  on their account.

[Footnote]   The Duhem-Quinean corporate-body doctrine  can be stated in terms of modus tollens, thus.  Given

            P1 + P2 + … Pn => Q

and

            ¬Q

we conclude

            ¬P1  ∨¬ P2 …  ∨  ¬Pn

That is, at least one of the co-conspirators whose conjunction led to a falsity, must itself be false.

But this does not imply  that the eventual valid conjunction will involve most or even any of those Pi;  we might even toss the whole lot of them overboard, and usher in a whole different set of conjuncts, to accomplish what we previously attempted with the P’s.  Such, roughly, describes the introduction of quantum mechanics, or the refutation of astrology, or any other paradigm-switch between incommensurables.

In his section on Quine-Duhem, Lakatos writes: 

Some people felt intuitively that the modus tollens from refutation  may ‘hit’ very distant premisses  in our total knowledge,  and therefore were trapped in the idea that the ‘ceteris paribus clause’ is a premiss which is joined conjunctively with the obvious premisses.  But this ‘hit’ is achieved, not by modus tollens, but as a result of our subsequent replacement of our original deductive model.

-- Imre Lakatos, “Morphology of Scientific Research Programs”, in I. Lakatos & A. Musgrave, eds., Criticism and the Growth of Knowledge (1970), p. 186

~

On a related note, another look at the notion that, should you ever derive a contradiction -- not as a tollentic hypothetical, but as the result of a deduction -- it’s Game Over for everything you’ve ever done.  A noted logician writes:

In an inconsistent system, every proposition is a theorem.

-- Hao Wang, From Mathematics to Philosophy  (1974), p. 42

Yet a few pages later  he qualifies this:

There is a generally accepted principle  that a contradiction implies everything.  We may yet distinguish proofs of the system which go through contradictions  from those which do not.

-- Hao Wang, From Mathematics to Philosophy  (1974), p. 47

~

Purely linguistic note:  A savorsome turn of phrase for the modal-tollentic move, one which I had not previously encountered:

Assume  towards a contradiction  that there is a set U  ∈ T that is not in T’.

-- Volker Runde, A Taste of Topology (2005),

~    ~     ~

There is a curious parallel, or at least an analogy, between, on the one hand,

(1) the foundational challenges to mathematics  alluded to above, together with, not a refutation of that challenge, but a broadly dismissive (and, arguably, pragmatically well justified) response on the part of professionals in the field;

and on the other hand

(2) recent broad-bore philosophical challenges to adaptationism (neo-Darwinism), along with the overall reaction of evolutionism’s professionals: indifference or -- the socio- and noö-politics of the thing being what they are -- foaming hostility.

Consider in particular  a recent (2010) volume co-authored by Jerry Fodor and Piattelli-Palmarelli, the well-written if pugnaciously titled What Darwin Got Wrong.

Their basic thesis is extensively and subtlely argued; hopefully I don’t overmuch crush it by fitting it into the following nutshell:

=>  The (currently hegemonic) gene-centered adaptationist theory  empirically does not work; indeed, for quite general reasons (having little to do with biology per se) it could not work even in principle;

=> A holistic, phenotype-cum-ecosystem-cum-kitchen-sink-centered approach  might -- might -- prove valid, at least in principle;  but in practice, the problem is intractable from a nomologically explanatory standpoint, apart from occasional lucky breaks.

Or, in the author’s own undistorted prose (p. 127):

To be sure, none of that actually shows that there aren’t laws of selection:  there may be, on the one hand, units of phenotypic change, and, on the other hand, units of ecological change;  and there may be laws that connect the two.  But there’s no reasons to suppose, as adaptationists routinely do, that the units of phenotypic change  are anything like what we generally think of as individual phenotypic traits.

(For connoisseurs of academic-polemical rhetoric, there is actually a sly move here.   While rhetorically conceding the possibility of a pheno-unit/eco-unit correlation, thus retrodictively legitimizing the latter two theoretical posits, these supposititious entities “units of ecological change” are by no means as familiar as other entities in the ontology of biology, and on the face of it  sound sort of bogus…)

~

We must distinguish two categories of challenge to any received body of doctrine:  The Anomaly; vs. Foundational.   The former (speaking just psychologically now) can either represent a mere annoyance  (or even:  Something to be hidden from the fickle general public at all costs, lest they overestimate its importance -- e.g.,  Evolution, Climate Change, anything medical), or a (possibly career-making) challenge.   The latter, to almost everyone, from the man in the street to the faculty lounge, tend to be just d*mned annoying.

Thus, consider  the Lasting Atom Scandal of the pre-quantum years, a poster-child example of Anomaly. (Nobody called it that, but  in all candor  they should have.)  This was phenomenologically egregious (in ways even a layman could understand), and had to be resolved somehow (some day, by someone else) -- indeed, imagine that the problem existed today, rather than a hundred years ago:  You’d have Republicans calling for the de-funding of physics, demanding e-mails archives, etc.  But it did not necessarily challenge -- certainly it did not set out to challenge, chin-foremost -- the nature of (say) Time, or Energy, or  for that matter  the existence of atoms (which had indeed been doubted by scientists, much later in history than most folks realize, but on quite different and less sophisticated grounds).

This anomaly, as we have seen, turned out to be handled in the most gratifying way possible:   We got to retain all the Maxwellian E-M we had laboriously learned, and now the new Quantum Mechanics stepped in (Jeeves-like)  to handle the anomaly.

More recently, there actually have been some challenges to physical theory  at a more basic level:  Time, which hoped to have escaped further challenge  by being subsumed into Space-Time, is once again on the carpet, from string theorists and others, who maintain that such parameters should fall out of a final theory, and not be input to it.  

Had such a challenge been posed, say, in the nineteenth century, it would have been an impudent kick at the foundations.  But now it (allegedly)  grows out of theory:  The theory may be mistaken, but it calls Time into question because it thinks it has something better. 

Much of the history of physics has been like that -- which is partly why it has been (politically) such smooth sailing.   Michaelson-Morley presented an Anomaly to the aether theory -- but no-one had been going around snarkily dissing ideas like distance and simultaneity until Special Relativity came along and re-conceived these.  This was (to use the Hegelian terminology, which here does fit) not a destruction, but a sublation  of the old ideas.

Sometimes there will be a simple anomaly, such as the discovery of continuous-but-nowhere-differentiable-functions, or space-filling curves.  These are eventually gobbled up and incorprated into a more robust and sophisticated mathematics.

Often an original sui-generis gnarly anomaly  will suggest a more general research program:  As, We need to pay closer attention to matterns of continuity and convergence (pointwise, uniform, almost-everywhere, etc., on the analytic side; and eventually the full exfoliation into the neighborhood-systems of topology).

Quite otherwise are challenges that come out of nowhere and that threaten to knock the stilts out from under you.  Russell’s Parodox, reaching Frege at press-time, did not strike him as another delightful puzzle to wrestle with some Sunday morning, but as a poisoned dart in his life-work.   Though they individually made numerous important positive contributions, the lytic work of Gödel and of Brouwer can be read this way, challenging the very notion of validity, truth, and proof.   Denial of the Excluded Middle indeed!  “Sirs, there you go too far!”  (“When you change the logic, you are merely changing the subject.” -- Quine, dyspeptically.)

Schematically (in your worst nightmare):

“Miller has reduced mathematics to set-theory;  and Spiller has shown that set-theory is rotten at its foundations.  Therefore everything that you are doing, or have ever done, or ever could do in your sorry life, is utterly worthless.”

Or:

(Pontius Pilate; Brouwer; post-Modernists):  “What is truth, anyway?  Huh? -- Meh.”

~

[Afternote]   It is a highly useful feature of the Blogspot interface, that it allows hot-linked Labels.    So for instance, were you disposed to read more by or about Mr. Hao Wang, for example, you would simply click on his name in the Labels field, and you will see every post so Labeled, in reverse chronological of posting.   But, annoyingly, there is a stringent limit on how many Labels any given essay is allowed.  We filled this one up with mathy stuff and now have no slack left over for the Darwiny bits.  So here you go:

http://worldofdrjustice.blogspot.com/search/label/adaptationism

http://worldofdrjustice.blogspot.com/search/label/philosophy%20%20of%20science

http://worldofdrjustice.blogspot.com/search/label/ultra-Darwinism

http://worldofdrjustice.blogspot.com/search/label/Charles%20Darwin

Note:  The last two are not redundant upon each other, and indeed have (I believe) zero overlap.  Darwin was not an ultra-Darwinist;  “Je ne suis pas marxiste” -- Marx.

Additional relevant Labels, which (boo, blogspot) would not fit into the Label field  for this post:
http://worldofdrjustice.blogspot.com/search/label/Ernest%20Gellner

[Post-Afternote]  Other examples of modus drasticus tollens.

A mittel-europäischer rationalist recalls “those golden, and, all in all very peaceful final decades of the colonial system”, and adverts ad the hermeneuts:

The argument seems to be -- Descartes led to Kipling.  We repudiate Kipling, so we must repudiate Descartes as well.   The expiation of colonialism must include the repudiation of clarity, for that had been but the tool of domination.

-- Ernest Gellner, Language and Solitude (posthum. 1998), p. 176

We, by contrast, raise a glass to Kipling;  so if this Descartes fellow had anything to do with it, chap can’t be all bad.

“During five literary generations, every enlightened person has despised him,  and at the end of that time  nine-tenths of those enlightened persons are forgotten, and Kipling is  in some sense  still there.” -- George Orwell, 1942

Modus tollens has surprisingly many enemies. Intuitionists, indeed, reject it:

The intuitionist position is that one can only state “P or Q” when one can give either a constructive proof of P  or a constructive proof of Q.  This standpoint has the consequence that proofs by contradiction (reductio ad absurdum) are not valid.

-- José Ferrerós, “The Crisis in the Foundations of Mathematics”, in Timothy Gowers, ed., The Princeton Companion to Mathematics (2008), p. 150

Holism à la Duhem-Quine  skirts it with a flanking maneuver:

… arguing that a given observational consequence is deduced  not from an empirical hypothesis alone, but rather from the conjunction of this hypothesis with the relevant set of auxiliary assumptions.   Hence, the failure of the observational consequence does not deductively refute the hypothesis by modus tollens, when taken by itself, but discredits only its conjunction with the pertinent auxiliaries.  

--  Th. Kupka, “Introduction”, in: Adolf Grünbaum, Collected Works, vol. I (2013), p. 2

~

Another example from a political context, where propositions are surrounded by swarms of sensitivities --  Re series of premises and conclusions relating ethnicity, nationalism, and industrialism:

The argument is impeccable.  Its premises are valid.  How can a valid inference from true premises  yield a conclusion which appears to be wholly refuted by historical reality?

Ernest Gellner, Nationalism (1997), p. 32

~

Quite different in purpose and detail from the classical modus tollens, is the assumption of a premise known to be contrary to fact, but where you have antecedently proven (at great expense of elbow-grease) that the assumption of this simple premise does not effect the results of calculations which otherwise must be carried out laboriously.  As, when (having slogged through a bit of integral calculus) you prove that, in calculating the gravitational effects of a ball, you can pretend that the entire mass of the ball is concentrated at the center:  an enormous simplification.  Or again:

We can get the correct answer for the probability of partial reflection  by imagining (falsely) that all reflection comes from only the front and back surfaces.

-- Richard Feynman, QED (1985), p. 107

The elegant idiom for introducing such a foredoomed hypothesis is “Suppose, per impossibile, ...”

~

At the antipodes from the “tollendus” camp, are the celebrants of falsification or falsifiability, associated  in particular  with the name of Karl Popper. ...

~

Miscellaneous additions: 

(1) Psychological observations

People seldom intuit what is unpalatable to them.  [Moreover, one can] eliminate any undesirable indirect implication of their special insight  by means of an additional hilfs-intuition, liquidating the embassassing logical relation.

-- Ernest Gellner, The Devil in Modern Philosophy (1974), p. 95

In short, one ‘answers’ the sceptic  by striding across logical gaps  to conclusions inconsistent with premises that one does not contest.

-- John Watkins, Science and Scepticism (1984), p. 34

(2) The reductio ad absurdum /”self-mate” gambit:

The traditional argument for the primacy of acceleration-retardation  rests on the absurdity of denying it.

-- Stephen Jay Gould, Ontogeny and Phylogeny (1977), p. 216

Chomsky’s book Syntactic Structures, which is regarded by some as a foundation-stone for this kind of activity, has been described by no less an authority than Roman Jakobson  as an argumentum a contrario (Jakobson, 1959), showing the impossibility of the whole enterprise.

-- Hilary Putnam, “Some Issues in the Theory of Grammar”, in  Mind, Language, and Reality (1975), p. 85

.

On “The Nature of Mathematical Knowledge” (enlarged)

That question is about as interesting as the nature of our knowledge of elephants.  We are interested in the zoology of elephants, not in the specificities of classroom biology lessons, or the economics of zoos.  We are uninterested in each blind man’s subjective and partial report upon the individual organs of these splendid creatures.

Mathematical knowledge, like pachydermal knowledge, is imperfect knowledge of something real that exists independently of us. By contrast, just which images we manage to form of these objects  are very much dependent upon ourselves – and to that extent, of interest only to unemployed social workers.

As our former math teacher put it:

Mathematics has a real content which transcends the inadequacies of our efforts to formalize it.

-- Andrew Gleason,  Fundamentals of Abstract Analysis (1966), p. v.

Or, from a philosopher:

For most mathematicians most of the time, having a feel for what is evident is important, but it is also enough: There is no further need for a theory of what that feel is.

-- Shaughan Lavine, Understanding the Infinite (1994)

*

Actually, it should not be deduced from the above, that I am somehow dissing our big friends the elephants.  A Theory of Elephants is considerably more promising than that idle grail of the physicists, a Theory of Everything.

The outstanding problem in the Theory of Elephants is the ontological status of BABAR – THE KING !!!!!

His Majesty ... The King !!!

An agnostic or non-Realist version, wilfully po-faced:

Our deductivist proposes clean answers to philosophical questions.  What is mathematics about?  Nothing … What is mathematical knowledge?  It is knowledge of what follows from what.  Mathematical knowledge is logical knowledge.

-- Stewart Shapiro, Thinking about Mathematics (2000), p. 150

*

*

There is a systematic ambiguity (roughly that of actio versus actum) to the term mathematics:

(I) The praxis of mathematizing.  This is a human pastime, comparable to needlework or basketball.

(II) The truths of mathematics.  Or, more or less synonymously: The real (though invisible) world.  These, in themselves, bear no dependency upon human practice or to any species whatever;  they existed before we were born.

The above may count as a polemical reformulation of roughly the dichotomy in the title of Hao Wang’s fine essay, “The Theory and Practice of Mathematics”.

*

In 1950, Raymond Wilder gave an address, “The Cultural Basis of Mathematics”, reprinted in  various places, and later wrote a whole book on the subject, Mathematics as a Cultural System (1981).   Bien-pensant commentors treat these with grave respect;  but the notion is practically nonsense.  For, if we take mathematics in sense (II) – the only sense of interest to us here – that is like saying “The cultural basis of elephants”:  there is none.  There is a cultural basis of circus stunts, of mouse- and peanut-myths, of Dumbo, but not of elephants themselves.  Their basis is their own four feet.

Why should the culture of mathematics  (necessarily, sensu I) – that is, the foibles of mathematicians – retain our attention?  The purely “human side” of mathematicians  is generally less interesting than that of country music stars.  A lot of mathematicians are pretty Asperger’s, frankly.
(For a poignant illustration of this, read The Genius in My Basement.)

There is, we grant, a certain interest in the sociology of mathematics, or in biographies of the great mathematicians. Intellectually, it is on a level with gossip about the off-court antics of basketball stars.  Fun, but of no mathematical (or basketball) interest.   It’s just a way for the mind to chew gum while it’s too exhausted to do anything substantial.  To get real, do math (or play basketball).

Not to come down too hard on the small geeky community that does follow the doings of math and physics whizzes; I number myself among them.   It would even be neat  if, instead of collecting baseball cards, people collected mathematician cards (“Trajea two Steven Smales for a John Milnor!”) .  -- By “people”, I here mean “eight-year olds”.

*

More interesting is the purported “reduction of mathematics to logic”.  It is not initially clear, however,  to what extent this program, if successful on its own terms, would enlighten us as to mathematics-sensu-(II), as opposed to the sense-(I) territory of our own mathematical formulations and formalizations (these being, after all, largely for mere convenience).  It might be more along the lines of the demonstration of the equivalence of the Heisenberg-style matrix-mechanics formulation with that of the Schroedinger-style wave formulation, of quantum mechanics. That feat didn't tell us all that much about the actual phenomena of physics,  apart from the fact that the world is a many-splendored thing, and can be described -- blind-man-fondling-elephant-fashion -- in a variety of ways.  It’s more like deciding whether today’s symposium shall be conducted in English or in French.

*

That said --

We argued here that the axiomatic method is cognitively post-hoc, and that  only in cases where (as with the Euclidean axioms) their positing is transparently motivated by our experience of the sensible world, is a top-down, axiomatic presentation  pedagogically sound.   Thus similarly in physics:

In lecture after lecture, and essay after essay,  Einstein began, not with an introduction to the subject at hand, but with an overview of how he’d arrived at that subject, or of how scientists in general  arrive at subjects in general. … For Einstein himself, the results of science had become incomprehensible without an understanding of the processes that led to them.

Richard Panek, The Invisible Century (2004), p. 153-4

C'est exact;  and the farther physics wanders from our human experience, and the father math develops beyond anything the world has seen before, the more necessary such a psycho-cognitive ladder does become.

*

Something like the dichotomy outlined above  must have been behind André Weil’s tart remark, in “History of Mathematics” (reprinted in Collected Works v. III as (1978b)):

Some universities have established chairs for “the history and philosophy of mathematics”;  it is hard for me to imagine  what those two have in common.

For:  the one is situated and contingent, the other timeless and beyond place.

*

Footnote:   These remarks about mathematics  apply  mutatis mutandis  to the Deity.  Deliberately confusing the distinction between truth and praxis, Karen Armstrong wrote a book -- a minor best-seller -- with the impudent title A History of God.  (At least she put A, not The; probably saved herself an extra millennium in Purgatory right there.)

*

Lakatos’ classic dialectical-dialogue Proofs and Refutations (you see the Hegel-style paradox already in the title), though focussing on the (as he persuasively argues, in the course of a detailed case-study spanning many decades) micro-level mess of actual mathematical progress, is yet Realist at its core:  the subtitle is “The Logic of Mathematical Discovery”, not “The Sociology of  ‘Mathematical’ Invention”.   We quoted him in another context  thus:

As far as naïve classification is concerned, nominalists are close to the truth when claiming that the only thing that polyhedra have in common  is their name.  But after a few centuries of proofs and refutations, as the theory of polyhedra develops, and theoretical classification replaces naïve classification,  the balance changes in favour of the realist.

-- Imre Lakatos, Proofs and Refutations (1976), p. 92

In an appendix to the main work, he offers a Hegelian formulation, one which (by the time the reader has progressed this far) has a certain paradoxical piquancy:

Mathematics, this product of human activity, ‘alienates itself’ [in the sense of Hegel and Marx] from the human activity, which has been producing it.  It becomes a living, growing organism, that acquires a certain autonomy [emphasis in original] from the activity that produced  it.  … The activity of human mathematicians, as it appears in history, is only a fumbling realisation of the wonderful dialectic of mathematical ideas.
-- Imre Lakatos, Proofs and Refutations (1976), p. 146

Plato, in his Paradise, smiles.

Math Porn

As we remarked earlier (Mathsex) the intersection of mathematics and literal pornography is a set of measure zero.   (A perhaps/perhaps-not  related fact, is that mathematicians themselves are entirely sexless.   They certainly do not reproduce biologically;  in fact, they do not even reproduce academically, most great mathematicians having been lousy lecturers -- and I mean really, really bad.  Instead, each individual mathematician-to-be  receives an Annunciation -- from which archangel, I alas do not know, never having received one, despite fervent prayers.)

Even “porn” in the journalistic sense, not of actual pornography, but of tawdry crowd-pleasing shallow presentations of deep subjects, seldom if ever is to be found in the same bar-booth with Mathematics.  (For a list of subjects that do so lend themselves to marketplace exploitation, consult our definitive document:  Funporn.)

Yet it is now our sad duty to report, that we have, for the very first time in our young life (young with respect to the afterlife, that is;  w.r.t. any of you-all whippersnappers, ancient), encountered an actual specimen of “math porn” (although in a very limited sense, as we shall see):  Popular Lectures on Mathematical Logic (sic, sic, sic), published in English in 1981, by the philosopher-logician Hao Wang.

There is a long tradition of lectures to the general educated public on scientific topics, by men preëminent in their field.  These were often later collected and published as volumes, sometimes with “Popular Lectures” in the title, by such true luminaries as Mach, Kelvin, Helmholtz (these in physics, though, note;  not mathematics).  The heyday for this activity was the late nineteenth century.   Their success presupposed a pool of educated laymen keenly interested in learning more about the intellectual forefronts of the day.

In America, the tradition survives sparingly, in university towns.   While our family lived in Princeton, I used to attend evening lectures at the IAS, held in their largest lecture hall.  Occasionally the audience was overflowing -- standing, or sitting on window-ledges.

Wang’s book likewise originated in public lectures -- though not perhaps to the general public, since they were given at the Chinese Academy of Science  (in 1977; translated  and published in English  four years later).   But by no stretch of semantics do they qualify as “Popular Lectures”, nor even as “Introductory Lectures for Logic Majors”.   (Of course, Wang himself may not be responsible for the English title of his book;  it may have been cooked up by some hunchbaked, drooling drone in the marketing department.)   Already on the eighth page of the introductory lecture, we read this (typical) passage:

Around 1960, Hanf numbers appeared, and Scott proved that measurable cardinals yield nonconstructable sets.  Results often mentioned as being impressive  are Morley’s theorem on categoricity in power, and applications to algebraic problems by Ax and Kochen.

Solovay soon proved the consistency without dependent choice  of the proposition that every set of reals is Lebesgue measurable.  (He has to assume that there are inaccessible cardinals;  it remains an open problem whether this stronger assumption can be avoided.

(There is no definition of any of these terms, like “inaccessible cardinals”, in early pages.  You’re supposed to already know this stuff.)   Now, for a non-specialist, it will be hard to judge just where that passage stands in the spectrum of difficulty;  but as a thumbnail comparison:  at Harvard, I took introductory logic in the philosophy department, and then straight logic in the math department, and we never got anywhere near these topics.

Lest  for some reason  Wang might have shoved all the hard stuff into the very first lecture, so as to clear the auditorium of lightweights, and become more pedagogical later on, I opened the book at random, happening upon this:

Exercise 2.  Find a direct proof of Corollary 1.3 without appeal to Lemma 1.1

You do not pose such homework in a “popular lecture”.  The book’s title amounts to false advertising  -- publishing-fraud.

~

The infraction perpetrated by the Wang book is minor -- a scattershot gallimaufry of sketches-for-an-idea-for-an-article on unrelated subjects, mislabeled as a popular introduction to a single subject -- and may well be laid at the door of the publisher rather than the author.    But now we must notice something more serious:  actual pandering to the public’s ignoble propensities, in the matter of math.  The book is titled The Math Instinct:  Why You’re a Mathematical Genius (Along with Lobsters, Birds, Cats, and Dogs), by Keith Devlin.

It has been well remarked, “As a rule, perjury in subtitles should be forgiven”.  This formulation was by Tony Rothman of Princeton, writing in American Scientist (March 2007), reviewing a biography by Siobhan Roberts, of the solid geometer Coxeter, King of Infinite Space, bone-headedly subtitled The Man Who Saved Geometry.  (It didn’t need saving, and he didn’t do it.)   But in the “Why You’re a Mathematical Genius” case, it is not just something tacked on by the publisher, it goes to the heart of the book:  “Devlin tries to make the subject less intimidating by demonstrating that math is all around us.”   That formulation is already cognitively-impaired;  “math” is all around us only in the sense that relativistic quantum mechanics is all around us.  Stuff is all around us, and a very few people (not you, not me) are able to make sense of some of it, somewhat (though less than is popularly assumed) by deploying a mathematical armamentarium:  neither Nature’s intricate hidden design, nor the occasional successes of experts, make you a mathematical “genius”.   And actually, few would be fooled by such transparent flattery (though it is of a left-handed sort, since the reader’s putative “genius” is, with the next breath, set at the level of lobsters);  one wonders why the publishers thought the public would be suckered-in by such fluff, rather than nauseated.   The answer no doubt is that such an approach is in tune with the general trend in America to “celebrate” one another’s narcissism.   That frame of mind does not make for keen exposition; as the reviewer in American Scientist remarks (Nov 2005, p. 572),

Devlin seems uncertain what his readers will need to have explained.  He reminds us that bats are mammals, but doesn’t define Ohm’s Law.

The case is the sadder since Devlin himself knows better.  He once wrote a very good semi-popular survey (only “semi-“, since equations do appear), Mathematics:  The New Golden Age (1999).   In this case, the rather grand subtitle is actually warranted: for while the great age of math as a handmaiden to physics is behind us, in the past half-century or so  it has effloresced to an astonishing extent as a multiply-connected enterprise in its own right -- with just enough new practical uses in cyptography and (if this one prove more than a dream) string theory, to keep it anchored.

~

It is now our happy privilege, likewise to report, that the other book occupying us this weekend, is precisely the opposite to the sugar-coating of the Wang packaging:  The title austere, uninviting;  the content as propaedeutic and intuitive as it is possible to be.  We refer, with reverence, to a book likewise originating in (semi-) public lectures (at UCLA, in the early 1980s):  Richard Feynman’s QED, published by Princeton in 1985.

The title might inspire a spurious sensation of familiarity:  quod erat demonstrandum, in which case it might fit a set of lectures on high school geometry.  But no, the acronym denotes something much more fearsome, something …. (but send the children to bed, before you scroll down)

…

…  nothing less than …

(horresco referens)

…

 =>  QUANTUM ELECTRO-DYNAMICS.

For years (decades, actually) I avoided this slender volume, though it stood on my shelves, owing to the misapprehension that, based on its titled subject-matter (which presupposed basic quantum mechanics) it must be significantly more difficult than the Big Red books, aimed at physics-major freshmen, on which I was weaned.  Yet not so.  Feynman, a master of exposition, offers the most intuitive account possible, of a highly non-intuitive subject.   Intuitive, yet not dumbed-down:  it takes a genius to tackle that.

But nota bene:   He never endeavors to coax you into thinking something is easier than it is, nor to flatter you that you have understood something when you have not -- both being common expository strategies of popularizers of science in this Age of Self-Esteem.

Rhetorically -- engagingly -- Feynman adopts the opposite strategy, hinting at what you are up against, though not bullying.  In the opening of the introductory lecture, he makes the quite accurate though socially/intellectually scandalous observation that

Everybody who comes to a scientific lecture  knows they are not going to understand it, but maybe the lecturer has a nice, colored tie to look at.

The second lecture, raising this observation to the status of a meme, opens thus:

This is the second in a series of lectures about quantum electrodynamics, and since it’s clear that none of you were here last time (because I told everyone that they weren’t going to understand anything), I’ll briefly summarize the first lecture.

The next begins:

This is the third of four lectures on a rather difficult subject -- the theory of quantum electrodynamics -- and since there are obviously more people here tonight than there were before, some of you haven’t heard the other two lectures  and will find this lecture almost incomprehensible.  Those of you who have heard the other two lectures  will also find this lecture incomprehensible,  but you know that that’s all right:  as I explained in the first lecture, the way we have to describe Nature  is generally incomprehensible to us.

This stance, though fey in a way, is yet preferable to that of the Theory-of-Everything charlatans who babble on about Beauty, implying that they can share their vision by mere dermatological osmosis.   There was one such on NPR’s science show last week  -- a string theorist yet, which is to say:  a specialist in a fashionable but drastically unintuitive math-packed would-be-physical theory, which, additionally, may well be actually wrong as a description of the real world -- or, worse, “not even wrong”.  But the interviewer kowtowed and pandered, and the interviewee luxuriated in his 15 famous minutes, as in a warm bubble-bath, complete with rubber duck.

A far more prominent string-theorist, Frank Wilchek, of the IAS, has a similar piece in a recent issue of Nature / Physics (Nature, by the way, seems to be in some ways following Scientific American down the path of corruption), calling on us all to “celebrate Beauty”.  -- By all means, say I, let us do so, and preferably in the altogether;  but don’t go calling it physics.

~

[Update & after-reflection]  The title (and thesis) of Devlin’s book are misconceived in a rather subtler and more substantial way than the undraped pandering of the subtitle:  The Math Instinct.     Because, in fact, there isn’t any.

I satirized the thesis that there is one -- honed, like the other instincts, by Natural Selection -- here:

The Urysohn Metrization Theorem:

an Adaptationist Account

However, the Ultradarwinians were not our real quarry in that sotie, but rather the mathematical Nominalists.

Devlin’s title echoes that of an earlier and much better work of scientific popularization, Steven Pinker’s The Language Instinct.   Here, the title is no mere gimmick from the marketing department:  the author is well aware that, properly understood (something that itself is no easy task), the positing of a language instinct constitutes a highly contentful, counterintuitive, scientifically testable, and in some quarters bitterly controversial hypothesis.   It is one that Chomsky and those in his intellectual wake  have been investigating with great ingenuity, for over half a century now.   They have made a telling case (though one that has become more difficult to understand as the theory itself advanced, rather the way Galilean mechanics are more intuitively accessible than Quantum Field Theory), one which need not here be passed in review.

With mathematics, matters lie quite otherwise. …

[To be continued, if reader interest warrants.  In the meantime, consult our counterthrenody to the thesis of universal mathematical genius:   Oligophrenia Mathematica.  ]

[Update Oct 2013]  Continued here.