The psychological theory of Sigwart shows itself in all its weakness when he seeks to give an account of the notion of “_existence_.” It has been already recognized by Aristotle, that this notion is gained by reflection upon the affirmative judgment. But Sigwart, like most modern logicians, neglects to make use of this hint. Instead of saying that to the existent belongs everything of which the affirmative judgment is true, he becomes repeatedly, and once more in the second edition of his logic (pp. 88-95) involved in diffuse discussions upon the notion of being and upon existential propositions, which cannot in any way conduce to clearness, seeing that they move in false directions. “To be,” according to Sigwart, expresses a relation (pp. 88, 95); if it be asked: What kind of a relation? the answer would, at first sight (92), appear to be, a relation to me as thinking. But no; the existential proposition asserts just this: “that the existing also exists, apart from its relation to me and to another thinking being.” It cannot, therefore, be “a relation to me as thinking.” But what other relation can be meant? Not until p. 94 is this brought out more clearly. The relation ought to mean (of course he adds “zunächst”, provisionally) the agreement (“identity” ib.) of the thing represented with a possible impression (“einem Wahrnehmbaren” ib. “something which may be perceived by me,” ib. p. 90). Now it will be immediately recognized that this notion of existence is too narrow; for it might very well be asserted that much exists which it is not possible to perceive, e.g. a past and a future, an empty space, and any sort of deficiency, a possibility or impossibility, etc., etc. It is therefore not surprising that Sigwart himself seeks to widen the notion. But he does this in a manner which I find it difficult to understand. At first sight he appears to say in order that something may exist it is not necessary that it can be perceived by me; it is enough if it can be perceived by anybody. Or what else can be meant when Sigwart, after what has just been said, that existence was the agreement of the thing represented with a possible impression, thus continues: “That which exists stands not merely _in this relation_ to me but to all other existing beings?” It cannot surely mean that Sigwart is inclined to ascribe to every existing being the capacity to receive every impression. It may be he only wishes to say that everything which exists stands to every other existing being in the relation of existence, and then it might be concluded from what immediately follows that this rather meaningless definition is intended to express that existence is the capacity to act or to be acted upon. (“What exists ... stands in causal relations to the rest of the world”; similar also is p. 91, note: the existent is something which “can exercise effects upon me and others.”)