Once more, and briefly, both datum and ideatum may (and positively, veritably, do) break up, each for itself, into physical and mental. In so far as the conviction gains ground that the earth revolves about the sun, the old fact is broken up into a new cosmic existence, and a new psychological condition--the recognition of a process in virtue of which movements of smaller bodies in relation to very remote larger bodies are interpreted in a reverse sense. We do not just eliminate the source of error in the old content. We reinterpret it as valid in its own place, viz., a case of the psychology of perception, although invalid as a matter of cosmic structure. Until we have detected the source of error as itself a perfectly genuine existence, we are not, scientifically, satisfied. If we decide that the snake is but a hallucination, our reflection is not, in purport, complete until we have found some fact just as existential as the snake would have been had it been there, which accounts for the hallucination. We never stop, except temporarily, with a reference to the mind or knower as source of an error. We hunt for a specific existence. In other words, with increasing accuracy of determination of the given, there comes a distinction, for methodological purposes, between the _quality_ or matter of the sense experience and its _form_--the sense perceiving, as itself a psychological fact, having its own place and laws or relations. Moreover, the old experience, that of sun-revolving, abides. But it is regarded as belonging to "me"--to this experiencing individual rather than to the cosmic world. Here, then, _within_ the growth of the thought-situation and as a part of the process of determining _specific_ truth under _specific_ conditions, we get for the first time the clue to that distinction with which, as ready-made and prior to all thinking, Lotze started out, namely, the separation of the matter of impression from impression as a personal event. The separation which, taken at large, engenders an insoluble problem, appears within a particular reflective inquiry, as an inevitable differentiation of a scheme of existence. The same sort of thing occurs on the side of thought, or meaning. The meaning or idea which is growing in acceptance, which is gaining ground as meaning-of-datum, gets logical or intellectual or objective force; that which is losing standing, which is increasingly doubtful, gets qualified as just a notion, a fancy, a prejudice, misconception--or finally just an error, a mental slip.