A Priori Knowledge and Rationalism

Some things we seem to know without consulting experience — that all bachelors are unmarried, that seven plus five is twelve — and the theory of a priori knowledge asks whether such knowledge is genuine, how it is possible, and whether reason is a source of substantive truth.

Definition

A priori knowledge is knowledge whose justification does not depend on sense experience but on reason or understanding alone; rationalism is the view that such knowledge is genuine and substantive, while empiricism restricts or denies it.

Scope

This topic covers the a priori-a posteriori distinction, the analytic-synthetic distinction, and the existence and explanation of a priori knowledge. It examines rationalist accounts that treat reason or rational insight as a source of substantive knowledge, empiricist attempts to confine the a priori to the trivially analytic, and Quine's radical challenge to the analytic-synthetic distinction itself. The broader empiricism-rationalism dispute frames the parent area; perception is treated separately.

Core questions

• Is there knowledge justified independently of experience?
• Does the analytic-synthetic distinction mark a real and principled divide?
• Can there be synthetic a priori knowledge, informative yet justified by reason alone?
• What faculty or insight could explain a priori justification?

Key theories

Kantian synthetic a priori

Kant distinguishes analytic from synthetic and a priori from a posteriori, arguing that mathematics and the principles structuring experience are synthetic a priori — substantive yet knowable independently of experience.

Quinean empiricism (rejection of the a priori)

Quine attacks the analytic-synthetic distinction and the dogma that some statements are immune to revision, concluding that no belief is held true come what may and that the supposed a priori has no principled basis.

Contemporary rationalism

BonJour defends rational insight as a genuine, fallible but irreducible source of a priori justification, arguing that even empirical reasoning presupposes a priori principles that cannot themselves be justified empirically.

History

The notion of a priori knowledge runs from Plato and the rationalists through Kant, whose category of the synthetic a priori was meant to secure mathematics and metaphysics. Logical empiricists tried to reduce the a priori to the analytic, but Quine's 1951 attack on the analytic-synthetic distinction challenged the whole framework. Late-twentieth-century rationalists such as BonJour mounted a defence of rational insight against this empiricist pressure.

Debates

Whether the analytic-synthetic distinction can bear epistemic weight

Empiricists hoped to explain all apparent a priori knowledge as analytic and so trivial, but Quine argued the distinction is not well founded, prompting rationalists to defend a robust, non-analytic a priori grounded in rational insight; the status of the distinction remains contested.

Key figures

• Immanuel Kant
• W. V. O. Quine
• Laurence BonJour

Seminal works

• kant-critique
• quine1951

Frequently asked questions

What does 'a priori' mean?

An a priori belief is one whose justification does not rest on sense experience but on reason or conceptual understanding alone. It contrasts with a posteriori knowledge, which depends on experience. Standard examples of candidate a priori knowledge are mathematics and logic.

What is the synthetic a priori?

It is Kant's category for judgements that are both informative, in that the predicate is not contained in the subject, and knowable independently of experience. Whether any such judgements exist is one of the central disputes between rationalists and empiricists.