But this distinction between _true_ and _false_, which remained unnoticed in the Categoriæ, comes into the foreground in the treatise De Interpretatione. The Proposition, or enunciative speech,[2] is distinguished from other varieties of speech (interrogative, precative, imperative) by its communicating what is true or what is false. It is defined to be a complex significant speech, composed of two terms at least, each in itself significant, yet neither of them, separately taken, communicating truth or falsehood. The terms constituting the Proposition are declared to be a Noun in the nominative case, as Subject, and a Verb, as Predicate; this latter essentially connoting time, in order that the synthesis of the two may become the enunciation of a fact or quasi-fact, susceptible of being believed or disbelieved. All this mode of analysing a proposition, different from the analysis thereof given or implied in the Categoriæ, is conducted with a view to bring out prominently its function of imparting true or false information. The treatise called the Categoriæ is a theory of significant names subjicible and predicable, fit to serve as elements of propositions, but not yet looked at as put together into actual propositions; while in the treatise De Interpretatione they are assumed to be put together, and a theory is given of Propositions thus completed. [Footnote 2: Aristot. De Interpret. p. 17, a. 1: [Greek: lo/gos a)pophantiko/s].] Words spoken are marks significant of mental impressions associated with them both by speaker and hearer; words written are symbols of those thus uttered. Both speech and writing differ in different nations, having no natural connection with the things signified. But these last, the affections or modifications of the mind, and the facts or objects of which they are representations or likenesses, are the same to all. Words are marks primarily and directly of the first, secondarily and indirectly of the second.[3] Aristotle thus recognizes these two aspects--first, the subjective, next the objective, as belonging, both of them conjointly, to significant language, yet as logically distinguishable; the former looking to the proximate _correlatum_, the latter to the ultimate. [Footnote 3: Ibid. p. 16, a. 3, seq. [Greek: ô(\n me/ntoi tau=ta sêmei=a prô/tôs, tau)ta\ pa=si pathê/mata tê=s psuchê=s, kai\ ô(=n tau=ta o(moiô/mata, pra/gmata ê)/dê tau)ta/.]] For this doctrine, that the mental affections of mankind, and the things or facts which they represent, are the same everywhere, though the marks whereby they are signified differ, Aristotle refers us to his treatise De Animâ, to which he says that it properly belongs.[4] He thus recognizes the legitimate dependence of Logic on Psychology or Mental Philosophy.