Descartes’ “indivisibility” argument

In the sixth of his Meditations on First Philosophy, Descartes writes:

[T]here is a vast difference between mind and body, in respect that body, from its nature, is always divisible, and that mind is entirely indivisible.  For in truth, when I consider the mind, that is, when I consider myself in so far only as I am a thinking thing, I can distinguish in myself no parts, but I very clearly discern that I am somewhat absolutely one and entire; and although the whole mind seems to be united to the whole body, yet, when a foot, an arm, or any other part is cut off, I am conscious that nothing has been taken from my mind; nor can the faculties of willing, perceiving, conceiving, etc., properly be called its parts, for it is the same mind that is exercised [all entire] in willing, in perceiving, and in conceiving, etc.  But quite the opposite holds in corporeal or extended things; for I cannot imagine any one of them [how small soever it may be], which I cannot easily sunder in thought, and which, therefore, I do not know to be divisible.  This would be sufficient to teach me that the mind or soul of man is entirely different from the body, if I had not already been apprised of it on other grounds.

This is Descartes’ “indivisibility argument” for dualism.  As with many of Descartes’ other arguments, I think both that it is not compelling as it stands, but also that it is much more interesting than it is often given credit for.  I devoted a few pages to the argument in Philosophy of Mind.  I won’t repeat here everything I said there. 

As Dale Jacquette interprets Descartes in his own book Philosophy of Mind, the argument can be summarized as follows:

1. My body is divisible into like parts (bodies)

2. My mind is not divisible into like parts (minds)

3. My body ≠ my mind

Jacquette’s reason for speaking of divisibility “into like parts” is that Descartes does not deny that we can distinguish different faculties within the mind, such as willing, perceiving, and conceiving.  What Descartes denies (on Jacquette’s reading) is that the mind can be divided into parts which are themselves minds.  The idea would be that you cannot divide a mind into parts that are like what you started out with (two or more minds), whereas you can divide a material object into parts that are like what you started out with (two or more material objects).  So, material things have a property that minds lack, viz. divisibility into like parts.  And thus, by Leibniz’s Law, the mind cannot be identified with a material thing.

Suppose we accept Jacquette’s reading.  What should we think of the argument?  It might seem at first glance that the argument fails with the first premise.  For isn’t it simply false to say of material things in general that they are divisible into like parts?  To be sure, if you divide a stone in half, you get two stones, and if you divide a piece of wood you get two pieces of wood.  But if you divide a human body in half, you do not get two human bodies; if you divide a car, you don’t get two cars; if you divide a circular object, you don’t get two circles; and so forth.  Indeed, even with stone and wood, if you keep dividing them you’ll eventually get to something that isn’t stone or wood.

But this objection is too quick.  Since Descartes was obviously aware of these facts, he cannot have meant that if you divide a human body you’ll get two human bodies, etc.  So what does he mean?  Recall that for Descartes, the essence of matter is to be extended in space.  Matter just is extension, and nothing but extension.  Thus when he says that body is divisible into like parts, what he means, no doubt, is that if you divide an extended thing the result will be two or more things that are also extended.  They may not be human bodies, specifically, or cars, or what have you, but they will be extended.  So, given Descartes’ conception of matter, it is certainly understandable why he would take the first premise to be true.

We’ll come back to that, but let’s turn for the moment to the second premise.  If for Descartes the essence of matter is extension, the mind is, on his view, essentially that which thinks to itself: I think, therefore I am.  It is the “I,” the ego, the self which remains in Meditation II after everything else has been doubted away by the end of Meditation I.  When Descartes (as Jacquette interprets him) says that the mind cannot be divided into like parts, I would suggest that what he means is that you can’t break an “I” or ego down into two or more “I’s” or egos, the way you can break an extended thing down into two or more extended things.

Why does Descartes think that the self or ego is indivisible in this way?  Note first that Descartes says that “when a foot, an arm, or any other part is cut off, I am conscious that nothing has been taken from my mind.”  He seems to be alluding here to the argument of Meditation I to the effect that it could in principle turn out that none of his “hands, eyes, flesh, blood [and] senses” are real, insofar as his belief that his body exists could be a delusion foisted upon him by an evil spirit.  The point, I take it, is not that his mind might in principle exist even if his body did not; that would be the thrust of his “clear and distinct perception” argument for dualism, and the “indivisibility” argument is presumably supposed to be an independent argument for dualism.  The point in the present context seems rather to be to give an example of something that might at first glance appear to be a part of the self which on reflection is not really part of the self at all.  An arm might seem to be a part of the “I” or ego, yet the “I” or ego can conceive of a situation in which it turns out that the arm does not exist, and perhaps never existed but was always only ever a hallucination, and yet where the “I” or ego nevertheless exists all the same.  Hence the arm isn’t really a part of the “I” or ego, but at best just something contingently attached to it.  And of course, if separated an arm certainly wouldn’t constitute another “I” or self all on its own.

But couldn’t there be a case of a mental (as opposed to bodily) part of the self which, if it were to be lost, would constitute another “I” or self that has split off?  In particular, don’t the phenomena associated with “dissociative identity disorder” and “split brain” patients provide evidence that this can happen?  As I noted in Philosophy of Mind, the significance of such phenomena has been greatly exaggerated.  How to interpret these cases is a matter of controversy, and in my view there is nothing going on in them that amounts to a single mind splitting into two, but merely a single mind becoming severely addled.  But suppose for the sake of argument that in some of these cases there really are two or more utterly distinct minds where previously there seemed to be only one.  Would Descartes have regarded this as a refutation of his thesis?

I think not.  Suppose you found yourself in a situation in which another mind suddenly seemed to be sharing control of your body.  Perhaps it would invade your thoughts and you would consciously struggle with it for control, like Steve Martin does with Lily Tomlin in the movie All of Me.  Or perhaps it would completely take over control for extended periods of time without your realizing what is going on, as in (too-late spoiler alert!) Fight Club.  Either way, I imagine Descartes would argue as follows: You could easily conceive of being rid of this second mind or self and carrying on “one and entire” without it, just as you can conceive of your “I” or ego carrying on “one and entire” in the absence of your arm or foot.  And in that case this other mind or self was never really a part of the “I” or ego at all, any more than the arm or foot was, but only something contingently associated with it.  Even if it seemed that it had “split off” from you, this would be an illusion.  It could only ever have been something contingently attached to you which you had belatedly become aware of, like a barnacle on a ship that has been attached to it for weeks before it is detected and scraped off.  For if this second self had ever really been a part of you, then you could not conceive of continuing “one and entire” without it.  You would instead be conceiving of a case where you persist in a diminished or incomplete way in the absence of this other mind or self.  But in fact what you are conceiving of is continuing in a complete way in the absence of something alien which had for whatever reason come to be attached to you.  A purported second “I” or ego which splits off from my “I” or ego is thus like the body: I can conceive of existing without it, and thus it is not really a part of the original “I” or ego at all.

If this is correct, then Descartes’ argument might seem to go through.  If the “I” or ego were a material (i.e. extended) thing, then since from any material thing you can split off a part that is itself a material thing, it should also be the case that you can split off from the “I” or ego a part that is itself an “I” or ego.  But that is not the case.  So the “I” or ego is not a material thing.

But not so fast.  The argument is still problematic, and, it seems to me, more because of what Descartes says about matter than because of what he says about the “I” or ego.  For one thing, the argument seems to presuppose that matter is infinitelydivisible, that no matter how far down you go in dividing a material thing you will always be able to divide the resulting parts further.  And indeed, that is precisely what Descartes thinks.  But that is, needless to say, a highly controversial assumption.  Suppose a critic opted instead for an atomist account of matter on which there is a bottommost level of material bits which cannot be divided further, or a corpuscularian theory on which there is a bottommost level that might in principle be divided further but in fact is not so divided.  Would that sink Descartes’ argument?

The Cartesian might respond as follows: Even if there is such a level, it would not help the materialist.  For the materialist wants to identify the self with some material object at the macro level -- in particular, with the brain.  And macro level objects like the brain are in the relevant sense divisible into like parts.  Hence the “I” or ego could not be identified with any of them.

The trouble with this reply, though, is that a materialist willing to think outside the box could decide to identify the “I” or self with an atom or corpuscle.  He could say: “I’m happy to think of the ego or self, as Descartes does, as akin to a Leibnizian monad -- as simple, undivided, or non-composite.  But unlike Descartes and Leibniz, I think it should nevertheless be identified with a material thing that is simple, undivided or non-composite.  It’s comparable to what Leibniz would call the ‘dominant monad’ of a system.  It’s the one atom or corpuscle in the human body that is associated with thought, and governs all the other, unthinking atoms or corpuscles that make up the body.” 

Needless to say, this materialist move would itself be problematic in several ways.  Why would some atoms or corpuscles be associated with thought while others are not?  How exactly does this one purportedly thinking material particle govern the rest? How could there be any material thing, however minute, that is in principle indivisible or non-composite?

But to address such questions would be to go well beyond what Descartes has to say in the indivisibility argument itself.  So, because such questions would need to be addressed -- and because I think Descartes’ own conception of matter is just wrong -- I think the “indivisibility” argument as it stands is not compelling.  But that doesn’t mean that there aren’t insights in it that couldn’t be developed into a better argument.  Indeed, we Aristotelian-Thomists would certainly hold that there is a sense in which any material substance can be decomposed into component parts (insofar as even the simplest or bottommost material substances are still going to be composed of substantial form and prime matter).  And Thomists also hold that there is a sense in which the soul is simple or non-composite (though of course it does not have the absolute simplicity that is unique to God). 

But spelling all this out would take us far from anything distinctively Cartesian.  And that is no surprise.  As I have noted in earlier posts (here, here, and here) what is of abiding value in Descartes’ arguments typically turns out to be the elements he borrowed from the Scholastic tradition that preceded him rather than the novelties he introduces.

Read More

Braving the web

The 10^thAnnual Thomistic Seminar for graduate students in philosophy and related disciplines, sponsored by The Witherspoon Institute, will be held from August 2 - 8, 2015 in Princeton, NJ.  The theme is “Aquinas and Contemporary Ethics,” and faculty include John Haldane, Sarah Broadie, and Candace Vogler.  Applications are due March 16.  More details here.

Does academic freedom still exist at Marquette University?  The case of political science professor John McAdams, as reported by The Atlantic, Crisis magazine, and Slate. 

The late Fr. Richard John Neuhaus is the subject of a new biography by Randy Boyagoda.  Review at National Review, and podcast of an interview with Boyagoda at Ricochet.

 
At Aeon magazine, Philip Ball comments on physics, philosophy, and “half-baked” ideas like the “many worlds interpretation” of quantum mechanics.

If “Bush lied, people died,” then why didn’t the Bush administration play up the WMDs it did find, so as to make the “lie” more plausible?  Don’t ask Jon Stewart.

New books in philosophy of religion: Gaven Kerr’s Aquinas’s Way to God, Paul O’Grady’s Aquinas’s Philosophy of Religion, and Fiona Ellis’s God, Value, and Nature.

Christopher Blum on how Aristotle invented science.

Philosopher Tom V. Morris has written high powered academic philosophy books and many popular works.  He also has a blog.

Philosopher Dennis Bonnette asks: Does Richard Dawkins exist?

But the New Atheism is old hat.  Here’s philosopher Philip Kitcher’s “soft atheism.”

Thomas Ward’s new book John Duns Scotus on Parts, Wholes, and Hylomorphism is reviewed by Robert Pasnau at Notre Dame Philosophical Reviews. 

Asimov’s Foundation is reviewed at Omni Reboot.  Better late than never.

Read More

Augustine and Heraclitus on the present moment

On the subject of time and our awareness of it, Augustine says the following in The Confessions:

But how does this future, which does not yet exist, diminish or become consumed?  Or how does the past, which now has no being, grow, unless there are three processes in the mind which in this is the active agent?  For the mind expects and attends and remembers, so that what it expects passes through what has its attention to what it remembers…

Suppose I am about to recite a psalm which I know.  Before I begin, my expectation is directed towards the whole.  But when I have begun, the verses from it which I take into the past become the object of my memory.  The life of this act of mine is stretched two ways, into my memory because of the words I have already said and into my expectation because of those which I am about to say.  But my attention is on what is present: by that the future is transferred to become the past. (Confessions11.28.37-38, Chadwick translation; an older translation is available online here)

So, it seems that for Augustine, for conscious awareness to “attend” to the present moment presupposes also both its “remembering” the immediate past and its “expectation” of the immediate future.  For example, when reciting the twenty third Psalm, my present awareness of speaking the words “…my shepherd…” has the significance and phenomenal feel that it does only because I simultaneously remember just having said “The Lord is…” and also simultaneously expect to follow the words I am speaking with “…I shall not want.”  Awareness of the present moment has intentionality in two directions: it “points” or is “directed” backwards toward the moment that preceded it, and forwards toward the moment that will succeed it. 

Augustine makes a similar point elsewhere, when he says that we cannot hear even a single syllable

unless memory helps us so that, at the moment when not the beginning but the end of the syllable sounds, that motion remains in the mind which was produced when the beginning sounded (De musica 6.5.10, quoted in Roland Teske, “Augustine’s Philosophy of Memory” in Stump and Kretzmann, The Cambridge Companion to Augustine, First edition)

This two-directional intentionality appears to be the key to our sense of the unity of the self over time.  Note that I say, not that it is the key to the self’s unity, but that it is the key to our sense of the self’s unity.  As I’ve said elsewhere, I think the self would in fact persist even if its memory of its past were obliterated.  What would be lost in that case is not its identity, but merely its knowledgeof its identity.  The Lockean idea that “who I am” is defined by my memories of the past and plans for the future is bad metaphysics, but it is good epistemology.  Such memories and expectations don’t constitute the self’s identity, but in normal cases (i.e. when one is not suffering from brain damage, mental illness, or the like) they will follow from and manifest its identity.  (They are, to use the Scholastic metaphysical jargon a little loosely, something like “proper accidents” of identity.)  The self’s remembrance of its distant past history and expectation of the carrying out of its long-range future plans is an extension of the memory of the immediate past and expectation of the immediate future of which Augustine speaks.

This two-directional intentionality in the subjective realm of the mind has a parallel in the objective world.  For the Scholastic metaphysician, the natural world is governed by the principle of finality and the principle of proportionate causality.  According to the principle of finality, efficient causes are “directed toward” or “point” forward to their characteristic effects, as toward a final cause.  And according to the principle of proportionate causality, effects “point” backwards, toward their efficient causes.  These principles are, to use Hume’s language (though not his principles), the “cement of the universe” that keeps things and events from being “loose and separate.” 

As I have argued many times, it was the early moderns’ abandonment of immanent final causality -- final causality as an inherent feature (as opposed to an observer-relative feature) of natural phenomena -- that paved the way for Humean skepticism about efficient causality.  As Aquinas argued, if efficient causes were not “pointed” or “directed toward” their characteristic effects, there would be no way to explain why those effects are in fact the ones which characteristically follow.  Things really would objectively be “loose and separate.”  (As usual, see Scholastic Metaphysics for detailed defense of all this Scholastic metaphysics.) 

If “directedness” did not exist even in the mind -- that is to say, if intentionality were an illusion, as eliminative materialism holds -- then the self’s sense of its own unity over time would also be undermined.  Just as the objective world breaks apart into innumerable disconnected distinct existences in the absence of final causality, so too does the subjective world break apart into innumerable disconnected distinct moments of awareness in the absence of intentionality.  Present awareness would not “point” backward to the immediate past or forward to the immediate future.  Its entire content would be limited to the present instant, and there would be no sense of a self that extended beyond that instant.

These implications of Humeanism and eliminativism are, of course, foreshadowed in Heraclitus’s philosophy, at least as traditionally interpreted.  For the Heraclitean, all is flux, and there are no abiding entities.  That includes the self.  There is no “I” that persists over time; there is only an awareness of the present instant followed by an awareness of the next instant followed by an awareness of the next, with no one abiding thing that has all of these awarenesses. 

Now, part of the significance of Augustine’s observation is that it indicates how the Heraclitean account is not true to the phenomenology of the sense of self.  We simply don’t perceiveourselves as existing merely in the present instant, for as Augustine points out, awareness of the present instant also involves in the normal case a remembrance of the past and an expectation of the future.  This two-directional intentionality is built into awareness of the present, and can be absent only when our cognitive faculties are malfunctioning. 

But there is a deeper lesson.  Augustine’s observation also helps us to see why the Heraclitean position cannot really be coherently formulated.  For suppose I try to think the thought that there is no abiding self.  As Augustine would point out, the words “…no abiding…,” as uttered inwardly to oneself, have their significance only insofar as I remember that they were preceded by an utterance of “There is…” and expect that they will be followed by an utterance of “…self.”  Now, these different utterances occur at different times, and are thus the objects of distinct acts of awareness.  But if the Heraclitean position is correct, there is no single abiding self that underlies these acts of awareness.  Thus there would be no one self that could have the thought that there is no abiding self.  The self that begins the thought would not be the same as the self which continues the thought, and neither would be the same as the self that completes the thought.  There would be nothing that actually has that particular thought.  Hence if Heraclitus’s position were correct, no one could so much as formulate it, for no one could last long enough to do so.  And yet we do formulate the position, as is evidenced by the fact that we can entertain it, argue about it, accept or reject it.  The very act of formulating Heraclitus’s position thereby refutes it.

So, Heraclitus was wrong.  How appropriate, then, that in the little montage above, Augustine seems to be hearing Heraclitus’s confession!

Read More

Accept no imitations

Given that he’s just become a movie star, Alan Turing’s classic paper “Computing Machinery and Intelligence” seems an apt topic for a blog post.  It is in this paper that Turing sets out his famous “Imitation Game,” which has since come to be known as the Turing Test.  The basic idea is as follows: Suppose a human interrogator converses via a keyboard and monitor with two participants, one a human being and one a machine, each of whom is in a different room.  The interrogator’s job is to figure out which is which.  Could the machine be programmed in such a way that the interrogator could not determine from the conversation which is the human being and which the machine?  Turing proposed this as a useful stand-in for the question “Can machines think?”  And in his view, a “Yes” answer to the former question is as good as a “Yes” answer to the latter.

This way of putting things is significant.  Turing doesn’t exactly assert flatly in the paper that machines can think, or that conversational behavior of the sort imagined entails intelligence, though he certainly gives the impression that that is what he believes.  (As Jack Copeland notes in his recent book on Turing (at p. 209), Turing’s various statements on this subject are not entirely consistent.  In some places he explicitly declines to offer any definition of thinking, while at other times he speaks as if studying what machines do can help us to discover what thinking is.)  What Turing says in the paper is that the question “Can machines think?” is “too meaningless to deserve discussion,” that to consider instead whether a machine could pass the Turing Test is to entertain a “more accurate form of the question,” and that if machines develop to the point where they can pass the test, then “the use of words and general educated opinion will have altered so much that one will be able to speak of machines thinking without expecting to be contradicted.”

This is very curious.  Suppose you asked me whether gold and pyrite are the same, and I responded by saying that the question is “too meaningless to deserve discussion,” that it would be “more accurate” to ask whether we could process pyrite in such a way that someone examining it would be unable to tell it apart from gold, and that if we can so process it, then “the use of words and general educated opinion will have altered so much that one will be able to speak of pyrite as gold without expecting to be contradicted.”  Obviously this would be a bizarre response.  Whether pyrite might be taken by someone to be gold and whether pyrite is in fact gold are just two different questions, and what I would be doing is simply changing the subject rather than in any way answering the original question.  How is Turing’s procedure any different?  And how exactly is “Can machines think?” any more “meaningless” than “Is pyrite gold?”

It’s no good, by the way, to object that the cases are not parallel insofar as an expert could distinguish gold and pyrite.  The cases are parallel in this respect, as Turing himself implicitly admitted.  Copeland points out (p. 211) that Turing elsewhere acknowledged that in a Turing Test situation, someone with expertise about machines might well be able to figure out from subtle clues which is the machine.  Turing thus stipulated that the interrogator should be someone who does not have such expertise.  He thought that what mattered was whether the ordinary person could figure out which is the machine.  So, whether an expert (as opposed to an ordinary observer) could figure out whether or not something is pyrite does not keep my example from being relevantly analogous to Turing’s.

So, why might Turing or anyone else think that his proposed test casts any light on the question about whether machines can think?  There are at least three possible answers, and none of them is any good.  I’ll call them the Scholastic answer, the verificationist answer, and the scientistic answer.  Let’s consider each in turn.

What I call the “Scholastic answer” is definitely notwhat Turing himself had in mind, though in fact it would be the most promising (if ultimately unsuccessful) way to try to defend Turing’s procedure.  The idea is this.  Recall that it is a basic principle of Scholastic metaphysics that agere sequitur esse (“action follows being” or “activity follows existence”).  That is to say, the way a thing acts or behaves reflects what it is.  A defender of the Turing Test could argue that if a machine acts like an intelligent thing, then it must be an intelligent thing.  But competent language use is a paradigmatically intelligent activity (especially for a Scholastic, who would define intellect in terms of the grasp of abstract concepts of the sort expressed by general terms).  Hence (so the argument might go) the Turing Test is a surefire way to test for intelligence.

But not so fast.  For a Scholastic, the principle agere sequitur esse must, of course, be applied in conjunction with other basic metaphysical principles.  And one of the other relevant ones is the distinction between substantial form and accidental form, a mark of which is the presence or absence of irreducible causal powers.  A plant carries out photosynthesis and a pocket watch displays the time of day, but these causal powers are not in the two objects in the same way.  That a plant carries out photosynthesis is an observer-independent fact about the plant, whereas that a watch displays the time of day is not an observer-independent fact about the watch.  For the metal bits that make up the watch have no inherenttendency to display the time.  That is a function we have imposed on them, from outside as it were.  The plant, by contrast, does have an inherent tendency to carry out photosynthesis.  That reflects the fact that to be a plant is to have a substantial form and thus to be a true substance, whereas to be a pocket watch is to have a mere accidental form and not to be a true substance.  The true substances in that case are the metal bits that make up the watch, and the form of a pocket watch is just an accidental form we have imposed on them.  (I have discussed the difference between substantial and accidental form in many places, such as here, here, and here.  For the full story, see chapter 3 of Scholastic Metaphysics.) 

Now, a computing machine is like a pocket watch rather than like a plant.  It runs the programs it does, engages in conversation, etc. in just the same way that the watch displays the time.  That is to say, it has no inherenttendency to do these things, but does them only insofar as we impose these functions on the parts that make up the machine.  (This is why, as Saul Kripke points out, there is no observer-independent fact of the matter about what program a computer is running, and why, as Karl Popper and John Searle point out, there is no observer-independent fact of the matter about whether something even counts as a computer in the first place.)  To be a computer is to have a mere accidental form rather than a substantial form.

In applying the principle agere sequitur esse, then, we need to determine whether the thing we’re applying it to is a true substance or not, or in other words whether it has a substantial form or merely an accidental form.  If we’re examining bits of metal and find that they display the time, it would silly to conclude “Well, since agere sequitur esse, it follows that metal bits have the power to tell time!”  For the bits are “telling time” only because we have made them do so, and they wouldn’t be doing it otherwise.  Similarly, if I throw a stone in the air, it would be ridiculous to conclude “Since agere sequitur esse, it follows that stones can fly!”  The stone is “flying” only because and insofar as I throw it.  Flying is, you might say, merely an accidental form of the stone.  What matters when applying the principle agere sequitur esse is to see what a thing does naturally, on its own, when left to its own devices-- that is to say, to see what properties flow or follow from its substantial form, as opposed to the accidental forms that are imposed upon it.

Now, seen in this light the Turing Test is just a non-starter.  To determine whether a machine can think, it simply isn’t relevant to find out whether it passes the Turing Test, if it passes the test only because it has been programmed to do so.  Left to themselves, metal bits don’t display time, and stones don’t fly.  And left to themselves, machines don’t converse.  So, that we can make them converse no more shows that they are intelligent than throwing stones or making watches shows that stones have the power of flight or that bits of metal qua metal can tell time.

So, while the Scholastic answer would (in my view, since I’m a Scholastic) be Turing’s best bet, at the end of the day it doesn’t really work.  But of course, Turing was no Scholastic.  Did he have in mind instead what I call the “Verificationist answer”?  The idea here would be this: The meaning of a statement is, according to verificationism, determined by its method of verification.  Now, we can’t peer into anyone else’s mind, in the case of human beings any more than in the case of machines.  So (the argument might continue), the only way to verify whether something is intelligent is to determine whether it behavesin an intelligent way, and intelligent conversation is the gold standard of intelligent behavior.  Hence the only way the question “Can machines think?” can be given a meaningful construal is to interpret it as asking whether machines can behave in an intelligent way.  Since that is precisely what the Turing Test seeks to determine, if a machine passes it, then there is nothing more that could in principle be asked for as evidence that it is genuinely intelligent.  Indeed (so the argument would go), there is nothing more for intelligence to be than the capacity to pass the Turing Test.

Now, verificationism was certainly in the air at the time Turing was writing.  It underlay the “philosophical behaviorist” view that having a mind is “nothing but” manifesting certain patterns of behavior or dispositions for behavior.  But there are serious problems with verificationism, not the least of which is that it is self-defeating.  For the principle of verification is not itself verifiable, which entails that it is, by its own standards, strictly meaningless.  If it were true, then it wouldn’t even rise to the level of being false.  Unsurprisingly, no one defends it any more, at least not in its most straightforward form.

But Turing does not in any case appeal to verificationism in the paper, and I don’t think that’s really what’s going on.  What I think he was at least tacitly committed to is what I call the “Scientistic answer” to the question of why anyone should think the Turing Test casts light on the question whether machines can think.  Turing’s view, I suspect, was essentially that there is no way to study intelligence scientificallyother than by asking what a system would have to be like in order to pass the Turing Test.  Hence that is, in his view, the question we should focus on.  Notice that this is not (or need not) be the same position as that of the verificationist.  His talk about “meaninglessness” notwithstanding, Turing need not say that it is strictlymeaningless to ask whether something could pass the Turing Test and yet not truly be thinking.  He could say merely that since there is no scientific way to investigate that particular question, there is no point in bothering with it, and we should just focus instead on what the methods of the empirical scientist might shed light on.

If this is what Turing is up to, then he is essentially doing the same thing Lawrence Krauss does when he pretends to answer the famous question why there is anything at all rather than nothing.  And what Krauss does, as I have discussed several times (here, here, here, and here), is to pull a bait-and-switch.  He pretends at first that he is going to explain why there is something rather than nothing, but then changes the subject and discusses instead the question of how the universe in its current state arose from empty space together with the laws of physics -- which, of course, are very far from being nothing.  His justification for this farcical procedure is essentially that physics has something to tell us about the latter question, whereas it has nothing to tell us about why there is anything at all (including the fundamental laws of physics themselves) rather than nothing.  What we should focus on, in Krauss’s view, is the question he thinks he can answer rather than the question we originally asked.

Now this is exactly the same fallacy as that of the drunk who insists on looking for his lost car keys under the lamp post, on the grounds that that is the only place where there is enough light by which to see them.  The fact that that is where the light is simply doesn’t entail that the keys are there, and neither does it entail that there is any point in continuing to look for the keys under the lamp post after repeated investigation fails to turn them up, or that there is no point in trying to find ways to look for the keys elsewhere, or that we should look for something else under the lamp post rather than the keys.  Similarly, the fact that the methods of physics are powerful methods doesn’t entail that those methods can answer the question why there is anything at all rather than nothing, or that we should replace that question with some other question that the methods of physics can handle, or that there is no point in looking for other methods by which to investigate the question.  To assume, as Krauss does, that the question simply must be one susceptible of investigation by physics if it is to be rationally investigated at all is to commit what E. A. Burtt identified as the fallacy of “mak[ing] a metaphysics out of [one’s] method” -- that is, of trying to force reality to conform to one’s favored method of studying it rather than conforming one’s method to reality. 

Turing seems to be guilty of the same thing.  Rather than first determining what thought isand then asking what methods might be suitable for studying something of that nature, he instead starts by asking what sorts of thought-related phenomena might be susceptible of study via the methods of empirical science, and then decides that those are the only phenomena worth studying.  The fallaciousness of this procedure should be obvious.  Characterizing “thought” as the kind of thing that a machine would exhibit by virtue of passing the Turing Test is like characterizing “keys” as the sort of thing apt to be found under such-and-such a particular lamp post.

In general, there is (as I have argued many times) simply no good reason to accept scientism and decisive reason to reject it.  There are at least five problems with it: First, formulations of scientism are typically either self-defeating or only trivially true; second, science cannot in principle offer a complete description even of the physical world; third, science cannot even in principle offer a complete explanation of the phenomena it describes; fourth, the chief argument for scientism -- the argument from the predictive and technological successes of science -- is fallacious; and fifth, the widespread assumption that the only alternative to natural science is a dubious method of doing “conceptual analysis” is false.  (See chapter 0 of Scholastic Metaphysics for detailed exposition of each of these points.)  So, the “Scientistic answer” also fails.

Needless to say, Turing was a brilliant scientist, and all of us who use and love computers are in his debt.  But his foray into philosophy resulted, I think, not in any positive contribution but only in an interesting and instructive mistake.

Read More