If only one of the factors is seen to be capable of existing without the other, and the latter to be such that it could not actually exist except as united with the former, so that the separability is not mutual, the distinction is regarded still as real, but only as a _minor_ or _modal_ distinction. Such, for instance, is the distinction between a body and its location, or its state of rest or motion: and, in general, the distinction between a substance and what are called its accidental modes or modal accidents. The distinction is regarded as real because reflection is held to assure us that it is in the reality itself independently of the mind, and not merely imposed by the mind on the reality because of some ground or reason in the reality. It is called a modal distinction rather than an absolute real distinction because those accidental modes of a substance do not seem to have of themselves sufficient reality to warrant our calling them “things” or “realities,” but rather merely “modes” or “determinations” of things or realities. It is significant, as throwing light on the relation of the virtual to the real distinction, that some authors call the modal distinction not a real distinction but a “distinctio _media_,” _i.e._ intermediate between a real and a logical distinction; and that the question whether it should be called simply a real distinction, or “intermediate” between a real and a logical distinction is regarded by some as “a purely verbal question.”(159) We shall recur to the modal distinction later (68). In the third place it must be noted that separability _in the sense explained_, even non-mutual, is not regarded as the _only_ index to a real distinction. In other words, certain distinctions are held by some to be real even though this test of separability does not apply. For instance, it is commonly held that not merely in man but in _all_ corporeal individuals the formative and the determinable principle of the nature or substance, the _forma substantialis_ and the _materia prima_, are really distinct, although it is admitted that, apart from the case of the human soul, _neither_ can actually exist except in union with the other. What is held in regard to _accidental_ modes is also applied to these essential principles of the corporeal substance: _viz._ that there is here a special reason why such principles cannot actually exist in isolation. Of their very nature they are held to be such that they cannot be _actualized_ or _actually exist_ in isolation, but only in union. But this fact, it is contended, does not prove that the principles in question are merely mentally distinct aspects of one reality: the fact that they cannot actually exist as such separately does not prove that they are not really separable; and it is contended that they are really and actually separated whenever an individual corporeal substance undergoes substantial change.