This, then, raises once more the question: What sort of “separation” or “separability” is the test of a real distinction? Is it separateness in and for sense perception, or separateness in and for intellectual thought? The former is certainly the fundamental index of the real distinction; for all our knowledge of reality originates in sense experience, and separateness in time and space, which marks its data, is the key to our knowledge of reality as a manifold of really distinct individual beings; and when we infer from sense-experience the actual existence of a _spiritual_ domain of reality we can conceive _its_ “individuals” only after the analogy of the corporeal individuals of our immediate sense experience. Scholastic philosophers, following Aristotle, have always taken the manifoldness of reality, _i.e._ its presentation in sense experience in the form of “individuals,” of “this” and “that,” “τοδὲ τι,” “_hoc aliquid_,” as an unquestioned and unquestionable _real datum_. Not that they naïvely assumed everything _perceived by the senses_ as an individual, in time and space, to be really an individual: they realized that what is perceived by sense as _one_ limited continuum, occupying a definite portion of space, may be in reality an aggregate of many individuals; and they recognized the need of scrutinizing and analysing those apparent individuals in order to test their real individuality; but they held, and rightly, that sense experience does present to us some data that are unmistakably real individuals—individual men, for instance. Next, they saw that intellectual thought, by analysing sense experience, amasses an ever-growing multitude of abstract and conceptually distinct thought-objects, which it utilizes as predicates for the interpretation of this sense experience. These thought-objects intellect can unite or separate; can in some cases positively see to be mutually compatible or incompatible; can form into ideal or possible complexes. But whether or not the _conceptually_ distinct, though mutually compatible, thought-objects forming any such complex, will be also _really distinct_ from one another, is a question which evidently cannot arise until such a complex is considered as an actual or possible _individual being_: for it is the individual only that exists or can exist. They will be _really_ distinct when found actualized in _distinct individuals_. Even the _conceptually_ one and self-identical abstract thought-object will be _really distinct from itself_ when embodied in distinct individuals; the one single abstract thought-object, “humanity,” “human nature,” is really distinct from itself in John and in James; the humanity of John is _really other_ than the humanity of James.