A priori is Latin for "from the former" or "from before", and may refer to:

David Hume (7 May [O.S. 26 April] 1711 – 25 August 1776) was a Scottish philosopher, historian, economist, and essayist, known especially for his philosophical empiricism and scepticism. He was one of the most important figures in the history of Western philosophy and the Scottish Enlightenment. Hume is often grouped with John Locke, George Berkeley, and a handful of others as a British Empiricist.

Beginning with his A Treatise of Human Nature (1739), Hume strove to create a total naturalistic "science of man" that examined the psychological basis of human nature. In stark opposition to the rationalists who preceded him, most notably Descartes, he concluded that desire rather than reason governed human behaviour, saying: "Reason is, and ought only to be the slave of the passions." A prominent figure in the sceptical philosophical tradition and a strong empiricist, he argued against the existence of innate ideas, concluding instead that humans have knowledge only of things they directly experience. Thus he divides perceptions between strong and lively "impressions" or direct sensations and fainter "ideas", which are copied from impressions. He developed the position that mental behaviour is governed by "custom"; our use of induction, for example, is justified only by our idea of the "constant conjunction" of causes and effects. Without direct impressions of a metaphysical "self", he concluded that humans have no actual conception of the self, only of a bundle of sensations associated with the self.

Immanuel Kant (German pronunciation: [ɪˈmaːnu̯eːl ˈkant]; 22 April 1724 – 12 February 1804) was a German philosopher from Königsberg (today Kaliningrad of Russia), who researched, lectured, and wrote on philosophy and anthropology during the Enlightenment at the end of the 18th century. At the time, there were major successes and advances in the sciences (for example, Isaac Newton, Carl Friedrich Gauss, and Robert Boyle) applying reason and logic.

Kant’s major work, the Critique of Pure Reason (Kritik der reinen Vernunft, 1781), aimed to unite reason with experience to move beyond what he took to be failures of traditional philosophy and metaphysics. He hoped to end an age of speculation where objects outside experience were used to support what he saw as futile theories, while opposing the skepticism of thinkers such as Descartes, Berkeley and Hume.

He stated:

Kant proposed a ‘Copernican Revolution’ in reverse, saying that:

Kant published other important works on ethics, religion, law, aesthetics, astronomy, and history. These included the Critique of Practical Reason (Kritik der praktischen Vernunft, 1788) and the Metaphysics of Morals (Die Metaphysik der Sitten, 1797), which dealt with ethics. And the Critique of Judgment (Kritik der Urteilskraft, 1790), which looks at aesthetics and teleology. He aimed to resolve disputes between empirical and rationalist approaches. The former asserted that all knowledge comes through experience; the latter maintained that reason and innate ideas were prior. Kant argued that experience is purely subjective without first being processed by pure reason. He also said that using reason without applying it to experience only leads to theoretical illusions. The free and proper exercise of reason by the individual was both a theme of the Enlightenment, and of Kant's approaches to the various problems of philosophy.