Formulating a rational defense of skepticism (a work in progress)

[Angrboda]

This is from Graham Priest's book, Beyond The Limits Of Thought, a text on dialetheism for the general reader. (If you don't have patience for philosophy, the main thrust of things can be got somewhat from the final section, starting with its third paragraph.)

There is one short section (two paragraphs) that includes some symbolic logic (rendered as an image, with red lines above and below). However, the content of these two paragraphs is not essential to understanding the whole, so feel free to skip them.

At one point I use the symbol '├' as a stand-in for the turnstiles, but the English language equivalent is also given. (x ├ y means y is provable from x)

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3.2 Sextus' argument for skepticism

Sextus compiled and polished all the arguments used for skepticism in both the streams of Greek skepticism. Many of the arguments are ad hominem, against various non-skeptics, and, in particular, the Stoics. However, the corner-stone of his skepticism was a very general argument based on the Tropes of Aenesidemus.

The Tropes are all arguments to the effect that the way things appear is dependent on such things as the sense-organs of the perceiver, other subjective factors, the context of perception, and so on. As a corollary, it follows that the same thing can be perceived in quite different, even contradictory, ways by different perceivers, or the same perceiver at different times. An object, for example, appears large when you are close to it, and small when you are far away. These arguments have largely been absorbed into Western philosophy, and are not now contentious.

What Sextus makes of them is, however, contentious. Sextus argues that because the world (i.e., what is the case) is perceived as different by different observers, one can never infer that the world is so-and-so from the mere fact that it appears so-and-so. What is needed, in addition, is some criterion to distinguish those appearances that are veridical from those that are not (Outlines of Pyrrhonism, I, 114):

For he who prefers one impression to another, or one 'circumstance' to another, does so either uncritically or without proof or critically and with proof; but [if he were to do it uncritically] ... he would be discredited. [So] ... if he is to pass judgment on the impressions he must certainly judge them by some criterion.

But now we have a problem. For we have reason to believe that the results of applying the criterion are correct only if we have reason to believe that the criterion itself is correct. And the criterion is not itself a statement of appearances; hence, if it is justified it must have some rationale or proof; and now the question arises as to what justification we have for believing that proof to be correct. Clearly, to appeal to the criterion at this point would be to beg the question (Outlines of Pyrrhonism, I, 117):

in this way both the criterion and the proof are involved in the circular process of reasoning, and thereby both are found to be untrustworthy; for since each of them is dependent on the credibility of the other, the one is lacking in credibility just as much as the other.

The only other possibility is that we must be able to give another proof of the correctness of this proof. But the question now arises as to the justification of this proof. Clearly, we are embarked on a regress; and if the regress is not to be terminated illicitly by appealing to the very criterion we were supposed to be justifying, it must go to infinity. But then it is vicious. For then there is no way that we could ever establish that the criterion, or any proof in the series, is correct (Outlines of Pyrrhonism, I, 122f.):

if he [who is trying to justify the criterion] asserts that the proof is true he will be asked for a proof of its truth, and again, for a proof of this latter proof, since it also must be true, and so on ad infinitum. But to produce proofs to infinity is impossible; so that neither by the use of proofs will he be able to prefer one sense-impression to another.

Thus, there is no way of justifying the claim that one set of appearances, as opposed to another, is a better indication of how things are. And hence there is no reasonable belief about how things are, as opposed to appear.

3.3 Analysis of the argument

Sextus' argument is an intriguing one. It has a major flaw, however. It assumes that our beliefs about how things are, are all obtained from our beliefs about how things appear to be, by applying some filter which lets through only the veridical perceptions. This assumption he took over from the Stoics; and its empiricism cannot be sustained. It can do no justice to our beliefs concerning, for example, mathematics or theoretical science.

However, this observation does not go to the heart of the matter, since there clearly are beliefs about the world that we have, and that we have in pretty much the way that Sextus supposes — at least in a 'rational reconstruction' of the process. For example, I believe that there is a flag on the pole of the building opposite that in which I write; and I believe this because I can see it out of the window. But even in this case Sextus' argument fails: I do have good (though by no means infallible) reason to suppose that there is a flag.

The flaw in Sextus' argument is, I take it, the claim that in order to have reasonable grounds for my belief I need some criterion which vouchsafes my perceptions. This is to misunderstand the relationship between experience and reason. Experience is always a reason for believing that the world is in such and such a way. It is a defeasible reason, and may be defeated by other things. The defeaters may be many and varied. We may know them in advance; for example, I may be aware that my perception at such distances is not reliable. Alternatively, we may learn them afterwards; for example, I may learn that the appearance of a flag is produced by a cunning hologram. If and when the defeaters arise, the experience ceases to be reasonable ground for the belief. But even though the evidence is defeasible, it is evidence, none the less, without further justification.

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The situation may be clarified by thinking of it in terms of non-monotonic logic. Non-monotonic inferences are inferences of the form:

α; there is no reason to suppose otherwise — so ß

In the case in question, α is of the form 'It appears to be the case that ß. Further information, γ, may turn up which does give us reason to suppose otherwise (that is, is a defeater). Hence, although we may have α ├ ß (ß is provable from α), we do not necessarily have α Λγ ├ ß (ß is provable from α _and_ γ), - which is the mark of a non-monotonic logic.

To illustrate the situation further, suppose that a hitherto unknown painting is discovered. In style and age it is a typical Rembrandt; it also bears what appears to be Rembrandt's signature. The painting appears to be a Rembrandt; and, no defeaters being known, we infer that it is a Rembrandt. But now suppose that a stroke-for-stroke identical picture turns up, and it is clear that at least one is a forgery, but that there is no indication as to which it is. Then this information provides a defeater for the former inference. Notice that the mere possibility of the existence of the doppelganger is not a defeater; but its actuality is. In a similar way, the Trope arguments of Sextus certainly establish that given any perception it is possible for things to appear different to another, or to oneself at a different time, but this is not sufficient to defeat the inference.

One objection to this kind of account is given by Lehrer ((1990), pp. 64f.), who argues that for the inference from 'It appears that ß' to ß to work (even non-monotonically), there must be some suppressed premises. For example, to infer that there is a flag on the mast of the building opposite, I must have information concerning what flags are like, etc. Thus, 'It appears that ß' can never on its own justify ß. (And the extra premises are not themselves statements of appearance; so the regress looms.) This, I think, misplaces the relationship of the role that the extra information plays with respect to the inference. The information is not required as a premise for the argument. (A young child, for example, might not even be able to articulate the information, but still makes the inference.) Rather, the information is that in virtue of which the inference is reasonable. In exactly the same way, the fact that a deductive argument is valid is not itself a premise of the argument; it is the fact in virtue of which the argument is reasonable (as was wittily exposed by Lewis Carroll (1895». If the inference is reasonable then its sole premise gives a reason for the conclusion. Why the inference is reasonable is a different question, and not one that needs to be answered before we know the premise to be a reason (any more than we must have a theory as to why modus ponens is valid before α and 'If α then ß' provide a reason for ß). Hence the regress is not generated.

It is worth noting that Sextus' argument does establish Carneades' form of skepticism, at least for certain kinds of claims. Just because the inference to how things are is non-monotonic, it is possible that a defeater may turn up, and so that we may have to retract our conclusion. It is not, therefore, certain. Put differently, if one takes the inference: it appears to be the case that IX; hence it is certain ·that IX; to be itself a non-monotonic inference, then the mere possibility of alternative perceptions, and all that this may entail, is a defeater for this inference. Hence it is never valid. Posterity has, in fact, strengthened this version of the skeptical argument. For we now have a much better understanding of the theory-dependence, and consequent fallibility, of observation; but I shall not pursue this matter here.

This is hardly a comprehensive discussion of the topic. However, it at least indicates where, I take it, the argument for Sextus' form of skepticism fails; which is sufficient for the present.

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3.4 Skepticism and self-reference



....Sextus would seem to be committed to this fact. After all, he spends several hundred pages giving reasons for skepticism. If he does not suppose that he is demonstrating that skepticism is rationally acceptable, what on earth does he think he is doing? We would therefore seem to have a contradiction of the kind characteristic of the limits of thought.

Sextus was aware of this. What was his response? He denied that the arguments show that skepticism is rationally acceptable (that is, the argument to Closure). He claimed that the arguments have rational force until they are deployed. At this point, however, they cease to have force, since they 'destroy themselves'. He put it as follows (Against the Logicians, II, 480-1):

there are many things which produce the same effect on themselves as they produce on other things. Just as, for example, fire after consuming the fuel destroys also itself, and like as purgatives after driving the fluids out of the body expel themselves as well, so too the argument ... can cancel itself also. And again, just as it is not impossible for the man who ascends to a high place to overturn the ladder with his foot after the ascent, so also it is not unlikely that the Sceptic after he has arrived at the demonstration of his thesis by means of the argument ... as it were a step ladder, should then abolish this very argument.

Sextus, then, tried to avoid the contradiction by explicitly bringing time into the issue. Before the force of the arguments is felt, they have force; after, they do not. This solution is not satisfactory. If he were talking about the persuasive content of the arguments — a purely psychological matter — then things could be as the metaphor of the ladder suggests; so that they are persuasive until they are seen to be self-undercutting, by which time their work is done. And Sextus does often talk of the arguments as therapeutic, advanced purely to have the desired psychological effect. But this reply is an ignoratio. For we were not talking about the persuasive power of the arguments, but about their rational force; and this is not a time-dependent matter. If Sextus' arguments worked then they would show that skepticism is rationally acceptable, contrary to his committed position that they are not.

A much better line for him to take would be simply to accept the logic of his own conclusion: that the arguments he uses have no rational force. Nor need this be as embarrassing as it at first appears. For he can quite consistently maintain that the arguments are all intended ad hominem against someone who does not accept skepticism. Against such people, who accept the premises of the arguments, the arguments must have rational force. Against people, such as skeptics, who do not accept the premises, they have no force. This line is advocated, successfully, by the modern-day Pyrrhonian, Feyerabend. In Against Method (1975), Feyerabend uses all kinds of arguments in support of a skeptical position; but he stresses that the arguments are ad hominem.

Sextus is not out of the woods yet, however. Even if he does not think that his arguments show skepticism to be rationally acceptable, he still maintains skepticism. And how can one maintain something that one does not hold to be rationally acceptable? To assert something involves taking on the commitment to support it with rational grounds for supposing it to be (objectively) true if challenged; if one refuses to do this, it voids the act of its social significance. To put it bluntly, such a person can legitimately be ignored. (The point is well argued in Brandom (1983).) By maintaining skepticism Sextus is therefore committed to the view that it is rationally defensible.

Sextus is well aware of this difficulty, too. His solution is simple; he denies that he maintains skepticism. He neither asserts nor denies it. In the state of epoche the skeptic neither asserts nor denies anything (Outlines of Pyrrhonism, I, 192):

Non-assertion ... is avoidance of assertion in the general sense in which it includes both affirmation and negation, so that non-assertion is a mental condition of ours because of which we refuse either to affirm or to deny anything.

Unfortunately Sextus now appears to be asserting something else (to the effect that he is not asserting anything); and this is equally contradictory. Sextus could maintain that he is not really asserting this either. But this would be (a) equally contradictory; and (b) disingenuous. For, in making this utterance, Sextus does intend us thereby to believe that he asserts nothing; and this is exactly what assertion amounts to. Hence, Sextus' attempts to avoid the contradiction at the limit of cognition work only by generating a contradiction at the limit of the expressible. His claim that he is not asserting anything is, by his own view, not something he is asserting (Transcendence). But he is asserting it (Closure). We have here, for the first time, a phenomenon that will become familiar: the attempt to avoid the contradiction at one limit of thought forces one into a contradiction at another.

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“Where am I, or what? From what causes do I derive my existence, and to what condition shall I return? ... I am confounded with all these questions, and begin to fancy myself in the most deplorable condition imaginable, environed with the deepest darkness, and utterly deprived of the use of every member and faculty.

Most fortunately it happens, that since Reason is incapable of dispelling these clouds, Nature herself suffices to that purpose, and cures me of this philosophical melancholy and delirium, either by relaxing this bent of mind, or by some avocation, and lively impression of my senses, which obliterate all these chimeras. I dine, I play a game of backgammon, I converse, and am merry with my friends. And when, after three or four hours’ amusement, I would return to these speculations, they appear so cold, and strained, and ridiculous, that I cannot find in my heart to enter into them any farther.”

— David Hume