Of course, if conceptually distinct thought-objects are seen to be mutually incompatible they cannot be found realized except in really distinct individuals: the union of them is only an _ens rationis_. Again it may be that the intellect is unable to pronounce positively as to whether they are compatible or not (18): as to whether the complex forms a possible being or not. But when the intellect positively sees such thought-objects to be mutually compatible—by interpretation of, and inference from, its actual sense experience of them as embodied in individuals (18)—and when, furthermore, it now finds a number of them co-existing in some one actual individual, the question recurs: How can it know whether they are _really distinct_ from each other, though actually united to form one (essentially or accidentally composite) individual, or only conceptually distinct aspects of one (simple) individual [27 (_b_)]? This, as we have seen already, is the case for which it is really difficult to find a satisfactory test: and hence the different views to be found among scholastic philosophers as to the nature of the distinctions which the mind makes or discovers _within the individual_. The difficulty is this. The conceptual distinction between compatible thought-objects is not a proof of real distinction when these thought-objects are found united in _one individual_ of sense experience, as _e.g._ animality and rationality in man; and the only distinction given to us by sense experience, at least directly and immediately, as undoubtedly real, is the distinction _between_ corporeal _individuals_ existing apart in space or time, as _e.g._ between man and man. How then, can we show that any distinctions _within the individual_ are real?