The Problem of Induction, and Does Science Have Presuppositions?

In a recent post I addressed the claim that science needs a philosophical or metaphysical grounding. Today I’d like to address the related subject of the “problem of induction”, and the following claims that are sometimes based on it:
– Science presupposes that “nature is uniform” or that “the future will resemble the past”.
– Science needs faith.

I’ll assume that you are already somewhat familiar with the problem of induction. If not, here are links to Wikipedia and SEP articles on the subject. For present purposes, I’ll take the conclusion of the argument to be as follows:

(1) We cannot give a justification for our most basic inductive practices.

Throughout this post, what I will mean by a “justification” is a justificatory argument. I limit the conclusion to our most basic inductive practices, because there is nothing circular about using more basic inductive practices to justify more advanced ones. For example, there is nothing wrong, necessarily, with the justificatory arguments that have been made in support of particular statistical methods, including Bayesian inference. (If there happens to be an error in some such justifications, it is not usually an error of circular reasoning.)

My response to (1) is to say that we don’t need any such justificatory argument. Why would anyone think that we do? The idea that we need such a justification, and that it’s a “problem” that we can’t have one, seems to arise because we’ve persuaded ourselves that we need justifications for everything we believe. But who persuaded us of that? If someone claimed, “We need a justification for every proposition we accept”, we should point out that that proposition seems self-defeating, as any justification of it will have premises that require further justifications, and so on ad infinitum. In any case, self-defeating or not, why should we accept it? If you ask me to accept the principle on the basis of an induction (e.g. “it’s always been useful to insist on justifications before”), then it’s self-defeating to use that principle to cast doubt on induction. If you accept that all our reasoning is rooted in induction (as the problem of induction seems to do), then it’s self-defeating to engage in any reasoning that casts doubt on induction. Just as it’s circular to argue for induction, it’s self-defeating to argue against it.

How did we get ourselves into this pickle? We’ve developed a habit of demanding and offering justifications, and that habit has become so inculcated that we’ve come to see justifications as an absolute requirement for appropriate belief (even a “metaphysical” requirement), when in fact they are just a tool that’s sometimes useful. After all, animals have appropriate beliefs, based on the evidence of their senses, despite never giving themselves any justifications. We humans too, throughout most of our waking hours, are forming appropriate beliefs about our immediate environment, without giving ourselves any justifications. Such beliefs are usually appropriate, because our automatic cognitive processes work reasonably well and give us reasonable beliefs based on the evidence of our senses. These processes mostly work automatically, without any discursive reasoning (verbal reasoning from proposition to proposition). And our basic inductive practices were themselves mostly acquired without discursive reasoning, through natural selection, experience and training. From birth we learn automatically from the school of hard knocks, and through natural selection we’ve learned from the hard knocks of our evolutionary ancestors.

Of course, we humans supplement our automatic inductive practices with discursively reasoned inductions. But note that even our discursive inductions make use of automatic induction: how else would we get from premises to a conclusion that isn’t deductively entailed? In any case, we tend to over-emphasise discursive reasoning, because that’s what we consciously observe ourselves using. We aren’t directly aware of the operation of our automatic non-conscious cognitive processes, and I suspect that until a couple of hundred years ago people had little inkling of the existence of such processes. Consequently, philosophers have traditionally tended to see discursive reasoning (or arguments) as the primary source of knowledge, and have attempted to root our knowledge in foundational arguments and foundational premises.

I claimed above that the practice of giving justifications is just a sometimes useful tool. Let me elaborate on that. One use of justifications, of course, is to persuade other people round to my way of thinking. Another is to make myself feel more satisfied about the beliefs I hold. Of more interest than those are what we might call truth-seeking uses, uses in which I genuinely attempt to improve the accuracy of my belief set, by critically scrutinising an existing belief. It can be useful to ask myself what justification I can give for a belief I hold, but I shouldn’t take the inability to find one as a decisive reason to reject the belief. Instead I should ask whether I have better reasons to reject a belief than to hold it. Being able to give a good justification is some reason for accepting or continuing to hold the belief, but it’s not necessarily decisive, since not all justifications are deductive proofs. (And even in the case of a mathematical proof, I could have made a mistake.) If I have no reason either to accept or to reject, then I have no reason to change my belief. And I have no reason to reject my basic inductive practices. I cannot argue against those practices in any way that does not depend on those practices. It’s just as self-defeating to doubt basic induction as it is circular to justify it.

My response to the problem of induction has similarities to Hume’s. According to the SEP:

Hume’s argument is often credited with raising the problem of induction in its modern form. For Hume himself the conclusion of the argument is not so much a problem as a principle of his account of induction: Inductive inference is not and could not be reasoning, either deductive or probabilistic, from premises to conclusion, so we must look elsewhere to understand it. Hume’s positive account does much to alleviate the epistemological problem—how to distinguish good inductions from bad ones—without treating the metaphysical problem. His account is based on the principle that inductive inference is the work of association which forms a “habit of the mind” to anticipate the consequence, or effect, upon witnessing the premise, or cause. He provides illuminating examples of such inferential habits in sections I.III.XI and I.III.XII of the Treatise(THN). The latter accounts for frequency-to-probability inferences in a comprehensive way. It shows that and how inductive inference is “a kind of cause, of which truth is the natural effect.”

I agree with this passage, except for the phrase “without treating the metaphysical problem”. First, the author seems to imply–on his own account–that there actually is a metaphysical problem. I deny that. What metaphysical problem? The idea that there’s a metaphysical problem seems to arise from the misguided ways of thinking that I’ve addressed above. Second, the author could be taken as implying that Hume believed there remained a metaphysical problem to be addressed. That may be so, though I’m not convinced. To be sure, Hume described his own solution to the problem of induction as a “skeptical solution”, but it’s not clear to me why he used the word “skeptical”. Presumably it indicates some sort of dissatisfaction with his solution. But what sort?

My statement (1) of the problem of induction referred to inductive practices. But sometimes the problem is cast in terms of beliefs, stated as propositions, on the grounds that induction involves reasoning from some such premise as “nature is uniform” or “the future will resemble the past”. In that case the problem may be stated in one of these forms:

(2) We cannot give a justification for our belief that nature is uniform.

(3) We cannot give a justification for our belief that the future will resemble the past.

As you might guess from what I’ve written above, my response to this is that we don’t need to reason from any such premise. Induction is not rooted in discursive reasoning, and in fact we rarely if ever observe anyone arguing from such a premise.

Do we in fact have such beliefs, even if we don’t use them as premises? I think what we (and animals) have is a tendency to learn from past experience by the basic inductive practices that I’ve discussed above. At a stretch, we could describe that state of affairs as our having a belief that nature is somewhat uniform, or a belief that the future will somewhat resemble the past, as long as we don’t take this to mean that we have some such proposition stored in our heads. (Do you think animals have those propositions stored in their heads?)

This brings me on to the claim that science presupposes that “nature is uniform” or that “the future will resemble the past”. The trouble is that such language is ambiguous. If we take it to mean that scientists must adopt such propositions as premises in their reasoning, then I reject that claim, for the same reasons I’ve given already. The inductive processes that scientists employ are not rooted in discursive reasoning, any more than are the inductive processes of the rest of us, or of animals. That’s why we don’t see scientists reasoning from that sort of foundational premise. But we could take the claim to mean only that scientists must proceed as if nature is (somewhat) regular, or as if the future will (somewhat) resemble the past. The claim is reasonable provided we interpret it that way, and accept that scientists proceed in that way because they have the inductive habits that they have, not because they are reasoning from a foundational premise.

Does any of this mean that scientists “need faith” to do science? Not really. Since we cannot sensibly question our most basic inductive habits, it makes little sense to say that we must have faith in them. We simply use them because we can do nothing else. We couldn’t stop using them even if we tried. But let me set aside the irrelevant problem of induction, and make a more general point. The expression “taking something on faith” is a rather fuzzy one, which is best seen as a matter of degree. We use it when we think someone has good reasons to subject their beliefs to skeptical scrutiny but fails to do so, or to do so sufficiently. In this matter of degree, science is just about as far towards the not-faith end of the spectrum as it’s possible to get. (Perhaps mathematics is even further.) Sure, individual scientists are fallible human beings, who sometimes fail to subject their scientific claims to sufficient skeptical scrutiny. But in general a very high priority is given to skeptical scrutiny in science, including scrutiny by testing against evidence. Contrast this with, say, religion, which lies far towards the opposite end of the spectrum, and where skeptical scrutiny of beliefs is often positively discouraged. Some believers do make some attempt to subject their religious beliefs to skeptical scrutiny. Again, I don’t want to make this an absolute distinction; it’s a matter of degree, and varies from person to person. But it’s also important to distinguish between the giving of justifications for one’s beliefs and skeptical scrutiny of those beliefs. Religious apologists may do plenty of the former while doing little of the latter. Indeed, that’s the normal human tendency. But the practices of science are aimed at minimising such truth-unfriendly tendencies. The practices of religions are not.

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