A Priori and A Posteriori

The terms "a priori" and "a posteriori" refer primarily to how or on what basis a proposition might be known. A proposition is knowable a priori if it is knowable independently of experience. A proposition is knowable a posteriori if it is knowable on the basis of experience. The a priori/a posteriori distinction is epistemological and should not be confused with the metaphysical distinction between the necessary and the contingent or the semantical or logical distinction between the analytic and the synthetic. Two aspects of the a priori/a posteriori distinction require clarification: the conception of experience on which the distinction turns; and the sense in which a priori knowledge is independent of such experience. The latter gives rise to important questions regarding the positive basis of a priori knowledge.

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Soren Kierkegaard

Søren Kierkegaard is an outsider in the history of philosophy. His peculiar authorship comprises a baffling array of different narrative points of view and disciplinary subject matter, including aesthetic novels, works of psychology and Christian dogmatics, satirical prefaces, philosophical "scraps" and "postscripts," literary reviews, edifying discourses, Christian polemics, and retrospective self-interpretations. His arsenal of rhetoric includes irony, satire, parody, humor, polemic and a dialectical method of "indirect communication" - all designed to deepen the reader’s subjective passionate engagement with ultimate existential issues. Like his role models Socrates and Christ, Kierkegaard takes how one lives one’s life to be the prime criterion of being in the truth. Kierkegaard’s closest literary and philosophical models are Plato, J.G. Hamann, G.E. Lessing, and his teacher of philosophy at the University of Copenhagen Poul Martin Møller, although Goethe, the German Romantics, Hegel, Kant and the logic of Adolf Trendelenburg are also important influences. His prime theological influence is Martin Luther, although his reactions to his Danish contemporaries N.F.S. Grundtvig and H.L. Martensen are also crucial. In addition to being dubbed "the father of existentialism," Kierkegaard is best known as a trenchant critic of Hegel and Hegelianism and for his invention or elaboration of a host of philosophical, psychological, literary and theological categories, including: anxiety, despair, melancholy, repetition, inwardness, irony, existential stages, inherited sin, teleological suspension of the ethical, Christian paradox, the absurd, reduplication, universal/exception, sacrifice, love as a duty, seduction, the demonic, and indirect communication.
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Rene Descartes

René Descartes’ major work on scientific method was the Discourse that was published in 1637 (more fully: Discourse on the Method for Rightly Directing One’s Reason and Searching for Truth in the Sciences). He published other works that deal with problems of method, but this remains central in any understanding of the Cartesian method of science. The common picture of Descartes is as one who proposed that all science become demonstrative in the way Euclid made geometry demonstrative, namely as a series of valid deductions from self-evident truths, rather than as something rooted in observation and experiment. Descartes is usually portrayed as one who defends and uses an a priori method to discover infallible knowledge, a method rooted in a doctrine of innate ideas that yields an intellectual knowledge of the essences of the things with which we are acquainted in our sensible experience of the world. This metaphysics of essences and the accompanying a priori method are then contrasted to the method of Newton, Bacon and the British empiricists, who denied the metaphysics of essences and the doctrine of innate ideas, and for whom knowledge of the world of sensible appearances was to be located, not by going outside it to a realm of essences, but by applying the method of experiment through which one could trace out the patterns in this world of causes and effects. There is something to this standard picture, but Descartes’ thought, like that of the empiricists, goes far beyond this simple description. In fact, Descartes sought to found our knowledge of things as much in experience and in experiment as in things a priori.
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Immanuel Kant

Immanuel Kant is one of the most influential philosophers in the history of Western philosophy. His contributions to metaphysics, epistemology, ethics, and aesthetics have had a profound impact on almost every philosophical movement that followed him. This portion of the Encyclopedia entry will focus on his metaphysics and epistemology in one of his most important works, The Critique of Pure Reason. (All references will be to the A (1781) and B(1787) edition pages in Werner Pluhar's translation. Indianapolis: Hackett, 1996.) A large part of Kant's work addresses the question "What can we know?" The answer, if it can be stated simply, is that our knowledge is constrained to mathematics and the science of the natural, empirical world. It is impossible, Kant argues, to extend knowledge to the supersensible realm of speculative metaphysics. The reason that knowledge has these constraints, Kant argues, is that the mind plays an active role in constituting the features of experience and limiting the mind's access to the empirical realm of space and time.
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