Teaching Theory of Knowledge

4. The Distinction Between A Priori and A Posteriori Knowledge

      The distinction between a priori and a posteriori knowledge, alternatively, between the truths of reason and the truths of sense, has been one of the crucial foci of modern philosophy. Even if the distinction has begun to blur in recent times, it is still important to the philosophies of mathematics and of language. Finally, the dispute between rationalism and empiricism helped shape modern science and philosophy. Hence the topic provides a unifying theme for historical reading and also introduces students to current issues. Some secondary texts that might prove useful are:

Wilson, M. Descartes. London: Routledge & Kegan Paul, 1982.

Rescher, N. Leibniz: An Introduction to His Philosophy. Oxford: Blackwell. 1979.

Stroud, B. Hume. London: Routledge & Kegan Paul, 1977.

Allison, H. Kant's Transcendental Idealism. New Haven. Conn.: Yale University Press, 1983.

      We suggest beginning with a brief consideration of Kant's distinction between a priori and a posteriori knowledge, since his statement of it is perhaps the clearest conceptually. Students are probably more familiar with a posteriori or experiential knowledge, so we turn to Plato for a dramatic statement of the primacy of a priori knowledge. The details of Plato's theory of knowledge are interesting and a challenge to naive empiricist sensibilities. Moreover, the mysterious quasi-religious quality of Plato's a priori knowledge provides an interesting subtext for later technical debates.

Readings

Kant. Introduction to The Critique of Pure Reason.

Plato. Meno, Republic (selections).

      Having thus set the stage, the study begins in earnest with the 17th century debate between rationalism and empiricism. Rationalists, like Descartes, Leibniz and Spinoza, stressed the primacy of reason as a method for understanding the world and so moved to a rationalistic conception of science as proceeding by a priori deduction and mathematical demonstration. A special virtue of rationalist doctrine was its ability to give an account of mathematics that seemed to accord with our intuitions. Since the development of science went hand-in-hand with the development of sophisticated mathematics, the rationalist account of mathematics was a strong point in their favor.

Readings

Descartes. Meditations, especially II, III.

Leibniz. New Essays, Book 3, chapter iii; Book 4; read the preface for a critique of Locke.

For further background, see the Leibniz-Arnauld correspondence.

      In contrast to the rationalists, the empiricists such as Locke, Berkeley and Hume maintained that all knowledge is acquired in experience and can be substantiated there. This kind of hard-headed philosophy seemed to work best for immediate perception and to square well with the stress on experimental methods in science. It was weaker, of course, in accounting for abstract ideas and general principles, especially those of mathematics.

Readings

Locke. Essay Concerning Human Understanding, Books 1, 4. Berkeley. Principles of Human Knowledge, Introduction.

Hume. A Treatise Concerning Human Nature, Book I, Parts 1

      Kant gave the best systematic development of a priori knowledge and the most plausible treatment, to that time, of the structures of mind needed to support such knowledge. It is important to stress his doctrine of synthetic a priori knowledge as a way of admitting experience without giving into the extremes of pure experience.

Kant. Prolegomena to Any Future Metaphysics, especially First and Second Part.

For further background, see The Critique of Pure Reason, Transcendental Doctrine of Elements through the First Division.

      Another synthesis of rationalism and empiricism, and an interesting contrast to Kant, was that of early Russell and the Vienna Circle. Using the logical tools of Frege and Russell to forge the mathematical structure rationalists had always demanded, this group then applied these structures to the empiricists' immediate experience in an effort to rationally reconstruct science. A priori knowledge was demystified, reduced through stages to pure logical knowledge and, eventually, to knowledge founded on convention. From synthetic a priori, philosophy returned to the analytic a priori.

Readings

Russell. Our Knowledge of the External World, II, III, IV.

Ayer. Language, Truth and Logic.

Cross References

For a discussion of the role of a priori knowledge in current discussions of epistemology, see also "A Priori Knowledge" in the "Contemporary Sources" section.

For an example of a course that considers whether recent results in linguistics support some version of a priori knowledge, see also "Language and Knowledge" in the "Bridge Courses" section.