| A PRIORI.—Reasoning from what is prior either as a condition of thought, or as a condition of existence—prior, logically or chronologically. (1) Reasoning from cause to effect (Aristotle); (2) from first truths, self-evident, and essential to intelligence; (3) from the forms of cognition which are independent of experience (Kant). According to Kant, à priori applies to forms of knowledge which are prior in logical order to experience. «The term à priori, by the influence of Kant and his school, is now very generally employed to characterise those elements of knowledge which are not obtained à posteriori—are not evolved out of factitious generalisations; but which as native to, are potentially in, the mind antecedent to the act of experience, on occasion of which (as constituting its subjective condition) they are first actually elicited into consciousness. Previously to Kant the terms à priori and à posteriori were, in a sense which descended from Aristotle, properly and usually employed—the former to denote a reasoning from cause to effect—the latter a reasoning from effect to cause. The term à priori came, however, in modern times, to be extended to any abstract reasoning from a given notion to the conditions which such a notion involved; hence, for example, the title à priori bestowed on the ontological and cosmological arguments for the existence of the Deity. The latter of these, in fact, starts from experience—from the observed contingency of the world, in order to construct the supposed notion on which it founds. Clarke’s cosmological demonstration called à priori, is therefore, so far, properly an argument à posteriori» (Sir W. Hamilton, Reid’s Works, p. 762).»There are two general ways of reasoning, termed arguments à priori and à posteriori, or according to what is usually styled the synthetic and analytic method; the one lays down some previous self-evident principles; and, in the next place, descends to the several consequences that may be deduced from them; the other begins with a view of the phenomena themselves, traces them to their original, and by developing the properties of these phenomena, arrives at the knowledge of the cause» (King, Essay on Evil, preface, p. 9).»Of demonstrations there are two sorts; demonstrations à priori, when we argue from the cause to the effect; and à posteriori, when we argue from the effect to the cause. Thus when we argue from the ideas we have of immensity, eternity, necessary existence, and the like, that such perfections can reside but in one being, and thence conclude that there can be but one supreme God, who is the cause and author of all things, and that therefore it is contradictory to this to suppose that there can be two necessary independent principles, the one the cause of all the good, and the other the cause of all the evil that is in the world; this is an argument à priori» (Dr John Clark, Enquiry into Evil, pp. 31, 32).»By knowledge à priori,» says Kant (Critique of Pure Reason, introd., sec. 1), «we shall in the sequel understand, not such as is independent of this or that kind of experience, but such as is absolutely so of all experience. Opposed to this is empirical knowledge, or that which is possible only à posteriori, that is, through experience. Knowledge à priori is either pure or impure. Pure knowledge à priori is that with which no empirical element is mixed up. For example, the proposition ‘Every change has a cause,’ is a proposition à priori, but impure, because change is a conception which can only be derived from experience.»»If there are any truths which the mind possesses, whether consciously or unconsciously, before and independent of experience, they may be called à priori truths, as belonging to it prior to all that it acquires from the world around. On the other hand, truths which are acquired by observation and experience are called à posteriori truths, because they come to the mind after it has become acquainted with external facts. How far à priori truths or ideas are possible is the great campus philosophorum, the great controverted question of mental philosophy» (Thomson, Outline of Laws of Thought, 2nd ed., p. 68; 3rd ed., p. 62).»It must be noticed that the term à priori has undergone important changes of meaning. In Aristotle’s philosophy, the general truth is ‘naturally prior’ (πρότερον τῇ φύσει) to the particular, and the cause to the effect; but since we know the particular before the universal, and the effect before we seek the cause, the particular and the effect are each prior in respect to us (πρότερον πρὸς ἡμᾱς)» (Anal. Post, I. 2 ; Top., VI. 4; Metaph. V. (Δ), XI. 1018, ed. Berol; Thomson’s Outlines of the Laws of Thought, 3rd ed., p. 68).— V. DEMONSTRATION. |
