Hume's Sceptical Argument Against Reason

HUME'S SCEPTICAL ARGUMENT AGAINST REASON In the section of the Treatise entitled Of scepticism with regard to reason Kume considers the mind as reflecting upon its own activities, monitors them as it were, and then adjusts them in accordance with certain principles and strategies. ^ What it discovers is that in drawing inferences, the mind sometimes errs. In the light of this knowledge, and in accordance with rational principles of epistemic probabilities , it adjusts its response to any inference it makes from one of certainty to one with epistemic probability of a degree somewhat less than certainty. But this rational adjustment is itself the consequence of an inference, which will be subject to the same qualifications . By repeating this process, it seems that all certainty reduces to probability and all probability to zero. Hume's argument begins this way: Our reason must be consider 'd as a kind of cause, of which truth is the natural effect; but such-a-one as by _ the irruption of other causes, and by the inconstancy of our mental powers, may frequently be prevented. By this means all knowledge degenerates into probability ; and this probability is greater or less, according to our experience of the veracity or deceitfulness of our understanding, and according to the simplicity or intricacy of the question. 2 It is important to be clear on the logical structure of this argument. Consider an actual case of inference. This produces a state of belief or affirmation. Hume does not say that the inference does not produce truth, i.e. , a true belief. But there is the possibility it does not. Nor is this a mere logical possibility. One can form the hypothesis about causes that this process of reasoning was in fact one which introduced an 91. element of error. One does not know that this hypothesis is true. But one does know that there is a certain probability that this causal hypothesis is true; as Hume puts it, it may frequently be true. Knowing that we have reasoned poorly sometimes (though not always) in the past, the hypothesis that we have on this occasion reasoned poorly has a certain probability , and we know this even though we have not verified the hypothesis for this particular occasion. On the basis of this unverified but nonetheless somewhat probable causal hypothesis we must as a matter of reason reduce the probability we attach to the belief or affirmation that was produced by the original inference. This reduction of probability is itself a matter of reasoning, however. Therefore about it, also, one can form the hypothesis that it is erroneous, and that the probability of the original affirmation was not reduced sufficiently. On the basis of this new hypothesis we must as a matter of reason reduce still further the probability of the first affirmation. And so on: as I reflect upon my use of reason, all the rules of logic require a continual diminution, and at last a total extinction of belief and evidence. (T183) The result here of the mind applying to its own activities what it discovers about itself is its ceasing to make any causal inferences. Feedback here yields the attitude of total scepticism, in the sense of rendering it reasonable that one ought totally to suspend judgment. To be sure, Hume does hold that no one is in fact such a total sceptic: Nature, by an absolute and uncontroulable necessity has determin 'd us to judge as well as to breathe and feel; nor can we any more forbear viewing certain objects in a stronger and fuller light, upon account of their customary connexion with a present impression , than we can hinder ourselves from thinking as long as we are awake, or see the 92. surrounding bodies, when we turn cur eyes towards them in broad sunshine. (T183) Inferences from sample to population cannot but be fallible, and this is the best we can do, given the logical gap between sample and population.The argument for scepticism with regard to reason concludes not only that such inferences are fallible, that they may be wrong, but more strongly that we have the strongest of reasons for supposing that they...