If, now, we take the above propositions—as they must be accepted as valid for all thinking beings in the system of rational psychology—in synthetical connection, and proceed, from the category of relation, with the proposition, "All thinking beings are, as such, substances," backwards through the series, till the circle is completed; we come at last to their existence, of which, in this system of rational psychology, substances are held to be conscious, independently of external things; nay, it is asserted that, in relation to the permanence which is a necessary characteristic of substance, they can of themselves determine external things. It follows that Idealism—at least problematical Idealism, is perfectly unavoidable in this rationalistic system. And, if the existence of outward things is not held to be requisite to the determination of the existence of a substance in time, the existence of these outward things at all, is a gratuitous assumption which remains without the possibility of a proof.
But if we proceed analytically—the "I think" as a proposition containing in itself an existence as given, consequently modality being the principle—and dissect this proposition, in order to ascertain its content, and discover whether and how this Ego determines its existence in time and space without the aid of anything external; the propositions of rationalistic psychology would not begin with the conception of a thinking being, but with a reality, and the properties of a thinking being in general would be deduced from the mode in which this reality is cogitated, after everything empirical had been abstracted; as is shown in the following table:
| 1 I think, |
||
| 2 as Subject, |
3 as simple Subject, | |
| 4 as identical Subject, in every state of my thought. |
