QUALITY. - Q. (πωλότης) signifies, in a generic sense, a mode of being. The universe, both material and spiritual, not only presents a multiplicity of entities (v. PLURALISM), but also various and mutable aspects, determinations, perfections (colors, sounds, weight, hardness..., thoughts, affections, virtues...), to which the generic term q. may refer.
In opposition to the atomists, who restricted their consideration to quantitative elements, Anaxagoras (v.) and Empedocles (v.) introduced the concept of q. in the explanation of phenomena. Plato treats q. as a fundamental idea (Theaet., 182 ff.); Aristotle considers it as the third of the supreme genera of being (Metaph., V, 7, 1017 a 25-30; I, 8, 8 b 25). St. Thomas (Sum. Theol., 1ª, q. 28, a. 2; 1ª-2ª, q. 49, a. 2) defines q. as a “modus essendi,” a “dispositio substantiae,” and distinguishes essential q., a determination of the very substantial being through form (v.), and accidental q., or q. properly so called, a further determination of the substance, really distinct from it (v. ACCIDENT; SUBSTANCE). Accidental q. is classified according to a fourfold distinction: 1) as a direct determination of the substance: habits (v.) and dispositions (science, virtue, vice, health, illness, supernatural virtue, Grace...); 2) as a principle of operation or activity: operative powers or faculties (senses, intellect, will...); 3) as a principle of alteration or passivity: sensible qualities; 4) as determinations of quantity: form and figure.
Descartes (v.) defines q. as a property of substance; it is twofold, thought, or q. of the spirit, and quantity, or q. of the body (Princ. philos., I, nn. 56 and 63; ed. Ch. Adam-P. Tannery, VIII, 26 ff.). In Kant, q. is one of the modes of judging to which belong the categories of reality, negation, and limitation (Critique of Pure Reason, Italian trans. by G. Gentile and G. Lombardo-Radice, I, Bari 1919, pp. 109 ff.). Hegel places q. as a moment in idea (v.); it is opposed to indeterminate being as the first and immediate determination and is again divided into pure being, determinate being, and being-for-self (The Science of Logic, Italian trans. by A. Moni, I, Bari 1924, pp. 72 ff.). In Bergson (L’évolution créatrice, Paris 1940, pp. 300 ff.), q. is a stable perceptual vision of real change and becoming, Boutroux (v.) affirms the qualitative element as essential to all reality (De la contingence des lois de la nature, Paris 1902, pp. 209 ff.).
Sensible qualities. - In philosophy, the problem of q. is particularly referred to sensible qualities. Already Indian thought had affirmed their subjectivity; among the Greeks, first the Eleatics and then the atomists considered them as fallacious and subjective appearances; Protagoras and Aristippus emphasized their relativity; Plato declares them objects of sensation and not of science (Theaet., 186). Aristotle (De an., II, 6-12) and later Scholasticism defend the objectivity of sensible qualities, distinguished into “primary” (hot and cold, dry and moist) and “secondary” or derived. In the period of the decline of Scholasticism (v.), much was discussed concerning the “qualitates occultae,” postulated to explain phenomena and natural forces: against these and against all sensible qualities, GALILEA (v.), Des-
Quail - Fall of the Manna, 5th century - Rome, Basilica of St. Mary Major.