The problem of a priori knowledge

The appearance of Quine's paper “Two Dogmas of Empiricism” in 1951 sparked a controversy which dominated that decade and remains alive to this day. The two dogmas are (1) the distinction of truths into analytic (linguistic) and synthetic (factual) and (2) reductionism, the thesis that isolated individual sentences have empirical significance. Quine's scepticism about these two notions constituted a heresy of sorts in the empiricist camp of which he was a member. To appreciate the significance of his apostasy and the disturbance it caused, a sketch is required of the status of orthodox empiricism and in particular its position on the problem of a priori knowledge. The problem arises from the incompatibility of two theses:

1. (1) The principle of empiricism: all knowledge is grounded in – justified by appeal to – experience.

2. (2) There is a priori knowledge, that is, knowledge independent of experience.

Mathematics and logic are cited as the prime areas in which we have a priori knowledge. In addition, many sentences whose content is neither purely logical nor mathematical are said to be known a priori:

The conflict is that if these sentences are known independently of experience, then they constitute an exception to the principle of empiricism and thus furnish a refutation of it. One traditional solution is rationalism, which accepts the existence of a priori knowledge and denies that all knowledge is empirical.