The Remaining Works of Benedictus de Spinoza

Whether or not this is the case is the very knot, the very cliff, which cannot be removed or moved by a conceived formal unity and that ideal identity of subject and object.

But it is nonetheless very easy to take the unity of the ideal object with the subject—which truly exists while you are thinking—for a real unity that is also necessary outside the form of thinking. Furthermore, it is easy for those who are primarily engaged in thinking, namely those philosophizing, to apply that necessary reduction of diverse things to unity, and the elevation of special reasons and laws to one principal reason—which they call the supreme principle—even to things insofar as they are forced to conceive of them as existing, that is, insofar as something is attributed to them by thought itself by which they are posited as existing outside of thought. If anyone makes this application fully and purely, he will reduce the το παν all in existing to το εν the one. For he has become accustomed in thinking to always considering two different things as one by a certain intuition; and thus, while he thinks, he proceeds to infinity. Now, therefore, he transfers (as indeed very similar things can be confused for some time even by the most sagacious) the formal method of thinking outside its own boundaries, that is, to the connection of existing things. He takes the law of thinking for the law of existing. Once this is obtained or granted, no system could ever be conceived as more true or more consistent with itself than that of Spinoza.