ACCIDENTE. — Etymologically, a. (from Lat. accidere = to happen; Gk. αυμβεβηκάς) is that which can be said of something but not necessarily (logical sense); it is that which inheres in something without constituting its substance (metaphysical sense). In its logical meaning, a. must be distinguished not only from that which constitutes the « species » (« the definition ») of a thing (= genus and difference), but also from the « property » (Ἰδιον), that is, from whatever follows « necessarily » (καθ'αὐτὰ) from the essence of something. In this sense Aristotle defines a. as that which is « indifferent » to the essence of something: ... id cui contingit inesse et non inesse uni eidemque, ut V. gr. « sedere » alicui uni (Top. I, 5, 102 b 4). Logical a. constitutes the last « predicable » (v.) of Porphyry’s well-known classification.
In its metaphysical meaning, a. is opposed to substance and embraces the whole sphere of being attributed
to the nine « categories » (κατῆγορίας, V. CATEGORIA) that follow substance and indicate the secondary contents and modes of being. A. is then everything that has no ontological consistency of its own and that, in order to « exist », needs to belong (« inhere ») to a substance as its proper foundation or real « substratum » (ὁποκείμενον): it is therefore a. a certain secondary reality or essence, destined to integrate and develop the principal reality of the substance on which it depends both for being and for existing. In this sense a. cannot be called « being », but rather « ens entis » and therefore « cuius esse est inesse »: Nam eus dicitur quasi esse habens, hoc autem solum est substantia, Accidentia autem dicuntur entia, non quia sunt, sed quia magis ipsis aliquid est; sicut albedo dicitur esse quia eius subiectum est album. Ideo non dicuntur simpliciter entia, sed entis entia, sicut qualitas et motus. (s. Tommaso, Comm. in XII Metaph. Arist., 1, 2419). Thus a. exists by virtue of the act of being of the substance and has as its property the « aptitudo ad subiectum », for which its definition is: « res cui debetur esse in alio » (s. Tommaso In IV Sent., dist. 24, q. I, a. 1, ad 2; cf. Sum. Theol., 3ᵃ, q. 77, a. 1, ad 2). In this intrinsic order, which a. have to substance, Aristotle and s. Tommaso see the possibility and unity of metaphysics as a science, insofar as the unity of being remains preserved and grounded. In this way the strongly dialectical relationship in which substance and a. stand to one another in the sphere of finite beings becomes manifest; for if substance can be called the support and also the cause of a., a. in turn constitute its acts and perfections: « unde et accidens forma dicitur » (s. Tommaso, Q. unica De virtutibus in communi, a. 3). It is, moreover, through a. that substance acts and is acted upon, and it is through the action of a. that generation and corruption, and all becoming both in the physical and in the spiritual world, are « prepared ».
From the phenomenological point of view — when one accepts with Aristotle that our knowledge necessarily develops in dependence upon experience — the first contents of consciousness refer to the accidental aspects of reality, and the essence, as such, constitutes only the final term of the inquiry that man conducts into the nature of things. This first phase of human knowledge, which Aristotle calls « induction » (v.), comprises the entire sector of the assimilation of the real by the human spirit that precedes and prepares the mature processes of abstraction and reflection. For, if it is true that the « middle » of the demonstration for discovering the properties of something and its ontological foundation is the essence of the thing itself, it is no less true that for us even a. « multum conferunt ad cognoscendum quod quid est » (De anima I, 1, 402b, 21 s).
In Scholasticism, the divisions of a. (absolute and modal, proper and common, intrinsic and extrinsic, etc.) developed and gave rise to very complicated discussions. The doctrine of a. is of fundamental importance for Catholic doctrine concerning certain mysteries of the faith (Grace, sin, the sacraments: in particular the Eucharist). In modern philosophy, and already in ancient and medieval subjectivism, the problem of a. was absorbed into that of the subjectivity of sensory qualities and the denial of the substantiality of being.