CRITERION. – From Greek κρίτριον, it is generally a norm or rule for recognizing and discerning (κρίνω = “I judge, I discern”) a thing, a fact, or a judgment. In philosophy it is most often 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 or instrument that serves or leads to knowledge of the truth is called a criterion: it is in this sense that reason, intelligence, conscience, and also reasoning, the syllogism, induction, etc., are sometimes called criteria. In the first and more proper meaning, the criterion is often identified with the motive of certainty, insofar as that which is a norm for discerning truth is also a principle determining certainty; consequently, the expressive value of the term is broadened, since the motives of certainty may be many and of various kinds. Thus one speaks of intrinsic and extrinsic, objective and subjective criteria, according as the motive of certainty is, or is held to consist in, a property inherent in the object of the 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, feeling).
The question of the criterion of truth was raised in the history of philosophy from the time when scepticism had denied the possibility of certainty, precisely because of the presumed lack of a sure and infallible norm by which to distinguish the true from the false (Sextus Empiricus, Adv. Math., VII, 195). Socrates, in opposition to the relativism of Protagoras, already thought he could point to a universal criterion of certainty in natural and common thought. Similarly, the Stoics sought a criterion of truth in those representations that are found equally among all human beings (κοινάι ἔννοια) and, because of their particular evidence, compel our assent (cf. N. Festa, I frammenti degli stoici, I, Bari 1932, pp. 33-36). But it was in modern philosophy, and still more after Kantian criticism, that the question underwent extensive development, with all its possible solutions. R. Cartesio 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 indestructible by reason; F. E. Jacobi in a spiritual feeling 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 (Labethonnière, Blondel) in the demands 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 the tradition that preserves and transmits divine revelation; F. Lamennais in the universal consent of humankind.
Traditional gnoseology does not deny the positive value of these criteria: authority as well as feeling, instinctive inclination, life, action, faith, and practical utility all play their part in facilitating and supporting intelligence in the knowledge of truth, which is often an achievement in which human beings must engage all their powers. But, once the primacy of intelligence is admitted, none of the criteria indicated can serve as the sole or ultimate criterion to which truth and certainty must appeal. There are undoubtedly in human beings states of certainty that arise and are founded, at least in part, on feeling, 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 (since it would be futile to seek a single criterion understood as an external infallible norm enabling us in every case to distinguish the true from the false), is, as St. Thomas already affirmed (In III Sent., dist. 23, I, 2, sol. 3), evidence, understood as the objective necessity of being and therefore of judgment. Certainly, evidence, taken in a general sense, and when its concept is not determined in relation to the metaphysical necessity of being, does not carry with it a universal guarantee of objectivity. In concrete knowing it may also be accompanied by subjective elements that represent its limitations and that only a complete commitment of the 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 event, at the foundation of all our certainty, even when it is brought into operation not through an exclusively intellectual or rational process (intuition and demonstration), but also through demands of an order not properly cognitive, such as spiritual experience, feeling, love, and action (v. EVIDENZA).