The Remaining Works of Benedict de Spinoza

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

But it is nevertheless very easy to consider the unity of the ideal object with the subject, which truly exists while you are thinking, as a real unity that is also necessary outside the form of thinking. It is further easy for those who are occupied primarily in thinking—namely, those philosophizing—to apply that reduction of diverse things to unity, which is necessary in the act of thinking or ἐνθυμήσει in internal reflection, 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 compelled to conceive of them as existing, that is, insofar as something is attributed to them by thought itself, by which they are posited as being outside of thought. If anyone does this fully and purely, he will reduce τὸ πᾶν the all in existing to τὸ ἓν the one. For he has become accustomed in thinking always to consider two different things as one by a certain intuition; and thus, while he thinks, he proceeds to infinity. Now, therefore, he transfers (just as things that are highly similar can be confused for some time even by the most sagacious) the formal method of thinking beyond 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 other system could be conceived that is more truthful and more consistent with itself than that of Spinoza.