The Scope of Knowledge
The far more difficult problem is that an inference to the best explanation defeats the sceptic only if we can defend the principle that underlies such inference against sceptical challenge.
We must be able to show that what appears to us to be a best explanation is likely to be true. In general, the most difficult part of any anti-sceptical epistemology will be to defend the fundamental principles of reasoning or the basic sources through which we seek knowledge. We have seen that we can defend perception as a source of knowledge through an inference to the best explanation.
Similar arguments will be available for memory, knowledge of other minds, and ordinary induction (for example, the best explanation for many coherent memory impressions will appeal to earlier veridical perception or testimony; the best explanation for an observed ratio of instances in a class may well be a deeper or universal regularity, and so on). But this leaves the formidable task of defending the principle of inference on the basis of which these other sources of knowledge can be defended.
In indicating the nature of this defence, we must note first that we cannot know a priori that such fundamental cognitive principles as inference to the best explanation lead to truth. This is not a necessary truth, since sometimes such inference fails; and whether it is generally reliable depends on the type of brains we have and on our relation to our environment. Nor can it be necessary that inference to the best explanation is likely to be reliable. It is hard to imagine how it could be necessary that anything is likely (contrast Bonjour 1998, p. 214).
In terms of the possible worlds model of probability, this would mean that in all galaxies or groups of possible worlds, the number of worlds in which the proposition in question is true exceeds the number in which it is false. But how could that be necessary and how could we know that it was: what is to keep the worlds in which the proposition is false from clustering?
In the absence of an a priori defence of inference to the best explanation and other fundamental cognitive principles and practices, we would require an inductive or empirical argument. One promising approach might be to argue that for creatures with such limited physical capacities and instincts as humans, basic cognitive capacities would have been naturally selected for their capacity to provide information or truth necessary to survival. It is plausible that humans would have had to infer correctly the proximity of predators from tracks or predator noises, for example, in order to survive, since they could not outrun them or otherwise protect themselves. There are three major obstacles that a generalised version of such an argument would have to overcome, however. First, there is the question whether, in the environment in which our brains evolved or were selected for their cognitive capacities, truth was in general the key determinant of fitness or utility. Second, a natural next question is whether an affirmative answer to the first one suggests that inferences to explanations far removed from the environment in which natural selection took place continue to be truth preserving. And third, there is the problem of circularity in the argument.
We can only very briefly indicate answers to the first two questions here, since we will pay more attention to the third, which will introduce the topic of the structure of knowledge. In regard to the first question, it must be admitted that systematic distortion can be utile and even fitness enhancing, as when the exaggeration of colour contrasts enables us to see object boundaries more easily (not to mention that the perception of colour in itself may be a systematic distortion of objective reality). But such systematic distortions seem to occur precisely to enable us to obtain more vital veridical information about the environment, for example about the locations of various objects. It remains hard to see how creatures like us could have survived if our basic cognitive capacities did not generate true information about our environments. We must know the means necessary to our ends, including survival, as well as the consequences of our actions, and all this is a matter of inferences as well as perception and memory.
As for inferences far removed from contexts in which survival is at stake, we can ask generally whether there is reason to suspect that a cognitive capacity that produces truth in one context will cease doing so in another. More specifically, we can separate everyday inferences that can be later verified directly in perception from those which produce the more remote products of scientific theory. The former inferences are demonstrated to be true if perception is accepted as a source of knowledge, but the charge of circularity will be raised again, to be addressed shortly. Scientific inferences not only take explanations to deeper levels, but seek to correct for distorting subjective inputs into earlier, commonsense explanations. This gives us more instead of less reason to believe in the truth of such explanations, although there might be less reason here to believe that the best of available explanations at a given time is the best overall, hence the true explanation.
The problem of circularity can be pressed at every stage of this suggested defence of inference to the best explanation as a basic cognitive principle. First, it was suggested that brains with such cognitive capacities to provide truths necessary to survival were probably products of natural selection. But theory of natural selection, indeed appeal to the physical environment, is itself legitimated via inference to the best explanation. The attempt to legitimate a principle by appeal to the products of its own use is circular. Second, we noted that many such inferences can be confirmed by later perceptions, giving direct evidence of their truth-preserving nature. But once more perception itself is certified as a source of knowledge only via inference to the best explanation for the ways things perceptually appear, again using the very cognitive principle that perception is supposed to help legitimate. Addressing this problem of circularity takes us to the question of the structure of knowledge, to which we now turn.
Fundamentals of Philosophy – Edited by John Shand