A priori knowledge

A priori knowledge is a term in philosophy used to describe anything that can be known from rational deduction rather than from observation or experience. The term derives from Latin words meaning "from what comes earlier" and was first used in Latin translations of the Elements—a textbook written by the Greek mathematician Euclid in about 300 BCE. The meaning that the phrase has subsequently acquired, however, originated in the Critique of Pure Reason by the German philosopher Immanuel Kant, first published in 1781. Examples of a priori knowledge are associated with mathematics, such as the statement that "the sum of 2 and 3 is 5," or with tautologies (self-referential statements), such as "all circles are round" or "it is what it is." If knowledge is unarguably true, in and of itself, it can be described as a priori: the term is therefore essential in identifying a crucial subcategory of knowledge.

Brief History

A priori knowledge has historically been contrasted with a posteriori knowledge. The latter term refers to knowledge requiring evidence, such as scientific principles, or the kind of understanding dependent on verification or experiment. As such, a priori and a posteriori are contraries. In philosophy, the broad idea of self-evident truth is found in works as early as those of ancient Greek thinkers such as Plato (fourth century BCE). The possibility of innate knowledge, independent of exterior proof, continued to be discussed from the Middle Ages through the Enlightenment of the seventeenth and eighteenth centuries, although seldom evidencing agreement on exactly what types of knowledge would qualify. During the Enlightenment, many thinkers, including French mathematician and philosopher René Descartes (1596–1650) and British philosophers John Locke (1632–1704), George Berkeley (1685–1753), and David Hume (1711–76) considered the question of a priori knowledge from the perspective of empiricism—in other words, the relation of knowledge to sense-data. However, there was no common consensus. The rationalist Descartes, for instance, held that the most important truths (as he saw it, those concerning God and the self) must derive from a priori knowledge. At the other end of the spectrum, Locke believed that no idea was innate: even apparently self-evident statements must originate in some form of experience of the world.

It was not until Kant brought together rationalist and empiricist perspectives in the Critique of Pure Reason that a workable identification of a priori knowledge was established. His account does not coincide exactly with the concept as it is normally used in the twentieth and twenty-first centuries, but it did provide the basic shape. For Kant, a priori knowledge is transcendental (above and beyond experience) and inbuilt into the mind. It requires no external proofs. All experience is shaped and determined by this antecedent a priori knowledge, and no other kind of knowledge is possible without it. Our whole perception of time and space, Kant argued, derives from this inherent structuring of the mind. That a priori knowledge is necessary to all other forms of understanding, therefore, was asserted by Kant in a way that guaranteed its importance to future generations of philosophers.

Overview

In epistemological terms (that is, in relation to the philosophy of knowledge), a priori knowledge refers to what is self-evidently true without proof or demonstration. This working definition has remained viable since Kant. In the Critique of Pure Reason, Kant asserts that a priori concepts are best understood as categories and that a priori judgments are principles. He further claims that some of these categories and principles are the fundamental building blocks of knowledge: they are the preconditions of what we call awareness and understanding. Examples of what Kant means by categories (a priori concepts) would be substance, cause, and interaction. An example of what he means by a principle (an a priori judgment) is that all experiences must have extension. In other words, anything experienced must have elements to it that extend either in time or space. This accounts for the a priori knowledge that between any two points in space, only one straight line is possible. Another such principle is that objects of sensation must possess relative magnitude. Someone feeling cold on a chilly day must know that the sensation of cold which they feel is a point on a scale—it could be warmer, or it could be colder. Similarly, the perception of color is an a priori judgment: a person identifying an object as orange rather than red or yellow is differentiating that object on a color spectrum, even though its color shades off into other colors on either side of its place on a scale without clear demarcations.

The usefulness of the term a priori has sometimes been questioned. The argument can be made that if a priori knowledge can only shed light on what is already understood through the operation of reason, it can never actually advance that understanding very far or meaningfully account for human experiences. It always loops back into itself in a circular way, offering no information about the world beyond the human mind. It may also be objected that there is no clear definition of what experience means in determining what is or is not a priori knowledge. Although these negative interpretations are valid, they do not fully represent the tools that a positive interpretation of a priori knowledge can bring to understanding the world. Since Kant, philosophers have generally sought to present a priori knowledge not only as a description of the mind's workings but also as a helpful capacity. An a priori perspective on the relative sizes or proportions of things, for example, would validate Kant's discussion of this kind of intuitive knowledge as usefully meaningful. If one can grasp that A is larger than B, one can, by the same token, grasp that B is larger than C—even if one has not experienced C. It is a priori knowledge that enables that cognitive leap. A priori knowledge continues to be recognized, accordingly, as a foundational component of human understanding.

Bibliography

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Casullo, Albert, and Joshua C. Thurow, editors. The A Priori in Philosophy. Oxford University Press, 2013.

DePaul, Micahel, and Amelia Hicks. “A Priorism in Moral Epistemology.” Stanford Encyclopedia of Philosophy, 12 May 2021, plato.stanford.edu/entries/moral-epistemology-a-priori. Accessed 14 Jan. 2025.

Greenberg, Robert. Kant's Theory of A Priori Knowledge. Penn State University Press, 2010.

Hanna, Robert. Cognition, Content, and the A Priori: A Study in the Philosophy of Mind and Knowledge. Oxford University Press, 2015.

Jenkins, Carrie. "A Priori Knowledge: The Conceptual Approach." The Bloomsbury Companion to Epistemology, edited by Andrew Cullison, 2nd ed., Bloomsbury, 2015, pp. 207-228.

Mares, Edwin. A Priori. Routledge, 2014.

Russell, Bruce. "A Priori Justification and Knowledge." Stanford Encyclopedia of Philosophy, 6 May 2020, plato.stanford.edu/entries/apriori. Accessed 14 Jan. 2025.

Shaffer, Michael J., and Michael L. Veber, editors. What Place for the A Priori? Open Court, 2013.