How wrongly Sigwart has analysed the notion of existence is also proved very simply by means of the following proposition: A real centaur does not exist; a centaur _in idea_, however, certainly exists, and that as often as I imagine it. Whoever does not clearly recognize here the distinction of the “ὂν ὡς ἀληθές i.e. in the sense of existing, from ὂν in the sense of real (wesenhaft) will I fear hardly be brought to recognize it by the fullest illustrations which might be furnished by further examples. We may, however, also consider briefly the following point: According to Sigwart, the knowledge of the existence of anything consists in the knowledge of the agreement of something represented in idea with, let us say, χ, since I do not clearly understand with what. What now is necessary in order to recognize the agreement of something with something else? Manifestly, the knowledge of everything which is required in order that this agreement should really exist. But this requires (1) that the one element exist, (2) that the other element exist, and (3) that between them there exist the relation of identity since what does not exist can be neither like something nor different from it. But the knowledge of the first element constitutes already in itself a knowledge of existence. Hence the knowledge of the two remaining elements is no longer necessary to the recognition of any existence, and Sigwart’s theory leads to a contradiction. (Cf. with what has been said here, Sigwart’s polemic against my _Psychology_, book ii. chap. vii. in his work; _The Impersonalia_, p. 50 seq., and _Logic_, vol. i. second edition, p. 89 seq. note, as well as Marty’s polemic against Sigwart in the articles: “Über Subjectlose Sätze” in the _Vierteljahrsschrift für wissenschaftliche Philosophie_, viii. i. seq.)[A]