Substance, therefore, is prior _in thought_ to accident; but is the substance itself also prior _temporally_ (prior _tempore_) to its accidents? It is prior in time to some of them, no doubt; the individual human being is thus prior, for instance, to the knowledge he may acquire during life. But there is no reason for saying that a substance must be prior _in time_ to _all_ its accidents;(252) so far as we can discover, no created substance comes into existence devoid of all accidents: corporeal substance devoid of internal quantity, or spiritual substance devoid of intellect and will. If prior in thought, though not necessarily in time, to its accidents, is a substance prior to its accidents _really_, _ontologically_ (prior _natura_)? Yes; it is the real or ontological principle of its accidents; it sustains them, and they depend on it. It is a passive or material cause (using the term “material” in the wide sense, as applicable even to spiritual substances), or a receptive subject, determined in some way by them as formal principles. It is at the same time an efficient and passive cause of some of its own accidents: the soul is an efficient cause of its own immanent processes of thought and volition, and at the same time a passive principle of them, undergoing real change by their occurrence. Of others it is merely a receptive, determinable subject, of those, namely, which have an adequate and necessary foundation in its own essence, and which are called _properties_ in the strict sense: without these it cannot exist, though they do not constitute its essence, or enter into the concept of the latter; but it is not prior to them in time, nor is it the _efficient cause_ of them; it is, however, a real principle of them, an essence from the reality of which they necessarily result, and on which their own reality depends. Such, for instance, is the faculty of thought, or volition, or speech in regard to man. The accident-mode of being is, therefore, a mode of being which determines a substance in some real way. Its _formal effect_ is to give the substance some real and definite determination: not _esse simpliciter_ but _esse tale_. With the substance it constitutes a concrete real being which is _unum per accidens_, not _unum per se_. The accident has no _formal cause_: it is itself a “form” and its causality is that of a formal cause, which consists in its communicating itself to a subject, and, by its union therewith, constituting some new reality—in this case a concrete being endowed with “accidental” unity. Accidents have of course, a _material cause_; not, however, in the sense of a _materia ex qua_, a material from which they are constituted, inasmuch as they are simple “forms”; but in the sense of a _subject_ in which they are received and in which they inhere; and this “material cause” is, proximately or remotely, _substance_.