**CRITERION** — From the Greek *χριστόφιλο*, it is generally a norm or rule for recognizing, discerning (*χρίνω* = I judge, discern) a thing, a fact, or a judgment. In philosophy, it is mostly identified with the *criterion of truth* and, in this case, designates the norm by which to distinguish the true from the false. But in a broader and somewhat improper sense, every means and instrument that serves or leads to the knowledge of the truth is called a *criterion*: in this sense, reason, intelligence, conscience, and even reasoning, syllogism, induction, etc., are sometimes referred to as criteria.
In the first and most proper meaning, the *criterion* is often identified with the motive of certainty, inasmuch as what is the norm for discerning truth is also the determining principle of certainty; consequently, the expressive value of the term broadens, as the motives of certainty can be many and of varied nature. Thus, one speaks of intrinsic and extrinsic, objective and subjective criteria, according to whether the motive of certainty consists in or is made to consist in a property inherent to the object of judgment (evidence); or instead in a norm external to it (divine authority, universal consent); or in a subjective modality of knowledge (the clarity of perception, taste, sentiment).
The question of the *criterion of truth* was raised in the history of philosophy from the time when skepticism had denied the possibility of certainty, precisely due to the alleged lack of a secure and infallible norm by which to distinguish the true from the false (Sextus Empiricus, *Adv. Math.*, VII, 193). Already Socrates, in opposition to Protagoras’ relativism, thought he could indicate a universal criterion of certainty in natural and common thought. And similarly, the Stoics sought a criterion of truth in those representations that are found alike in all men (*χοιναί ἐγνοιαι*) and, by their particular evidence, compel our assent (cf. N. Festa, *I frammenti degli stoici*, I, Bari 1932, pp. 33-36). But it is in modern philosophy, and even more after Kantian criticism, that the question has received extensive development, with all possible solutions. R. Descartes placed the ultimate criterion of certainty in clear and distinct perception; E. Spencer in the inconceivability of the contradictory; T. Reid in common sense, which leads us almost by instinctive necessity to affirm certain principles indissolubly linked to reason; F. E. Jacobi in a spiritual sentiment that, prior to and beyond every intellectual perception, assures us of the truth; pragmatism (W. James) in the function of utility or necessity that a proposition or doctrine demonstrates for life; voluntarism (Ch. Renouvier) in the free affirmation of the will; immanentism and actionism (Laberthonnière, Blondel) in the exigencies of life and action. Meanwhile, another current sought the criterion of certainty in an external norm: P. Huet in the authority of divine revelation; L. de Bonald in tradition, which preserves and transmits divine revelation; F. Lamennais in the universal consent of the human race.
Traditional epistemology does not deny the positive value of these criteria: both authority and sentiment, instinctive inclination, life, action, faith, and practical utility have their part in facilitating and aiding intelligence in the knowledge of truth, which is often an achievement in which man must engage all his faculties. But, granted the primacy of intelligence, none of the indicated criteria can serve as the sole or ultimate one to which truth and certainty must appeal. There are undoubtedly in man states of certainty that arise and are founded, at least in part, on sentiment, such as, for example, aesthetic certainty; but if one remains within the field of intellectual knowledge, the supreme criterion, in the sense of the universal motive of certainty (for it would be vain to seek a single criterion, understood as an infallible external norm that allows us to discern the true from the false in every case), is, as St. Thomas already affirmed (*In III Sent.*, dist. 23, I, 2, sol. 3), *evidence*, understood as the objective necessity of being and hence of judgment. Certainly, evidence, taken in a generic sense and unless its concept is determined in function of the metaphysical necessity of being, does not carry with it a universal guarantee of objectivity. It can also be accompanied, in concrete knowing, by subjective elements that represent its limits and that only a total commitment of human spiritual energies can overcome. It is in this sense that a positive value must be recognized in the criterion of "convergence," recently advocated by A. Brunner. But evidence is, in any case, at the root of all our certainty, even when it is actualized not solely through intellectual or rational processes (intuition and demonstration) but together with instances of a non-cognitive order, such as spiritual experience, sentiment, love, and action (v. EVIDENCE).
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