Why philosophy

We are now in a position to see that the function of philosophy is wholly critical. In what exactly does its critical activity consist?
One way of answering this question is to say that it is the philosopher’s business to test the validity of our scientific hypotheses and everyday assumptions. But this view, though very widely held, is mistaken. If a man chooses to doubt the truth of all the propositions he ordinarily believes, it is not in the power of philosophy to reassure him. The most that philosophy can do, apart from seeing whether his beliefs are self-consistent, is to show what are the criteria to determine the truth or falsehood of any given proposition : and then, when the sceptic realises that certain observations would verify his propositions, he may also realize that he could make those observations, and so consider his original beliefs to be justified. But in such a case one cannot say that it is philosophy which justifies his beliefs. Philosophy merely shows him that experience can justify them.

A J Ayer. 1936. Language, Truth and Logic. London: Victor Gollancz.