Introduction

1. There is a twofold operation of the intellect, as the Philosopher says in III De anima. One is the understanding of simple objects, that is, the operation by which the intellect apprehends just the essence of a thing alone; the other is the operation of composing and dividing. There is also a third operation, that of reasoning, by which reason proceeds from what is known to the investigation of things that are unknown. The first of these operations is ordered to the second, for there cannot be composition and division unless things have already been apprehended simply. The second, in turn, is ordered to the third, for clearly we must proceed from some known truth to which the intellect assents in order to have certitude about something not yet known.

             2. Since logic is called rational science it must direct its consideration to the things that belong to the three operations of reason we have mentioned. Accordingly, Aristotle treats those belonging to the first operation of the intellect, i.e., those conceived by simple understanding, in the book Praedicamentorum; those belonging to the second operation, i.e., affirmative and negative enunciation, in the book Perihermeneias; those belonging to the third operation in the book Priorum and the books following it in which he treats the syllogism absolutely, the different kinds of syllogism, and the species of argumentation by which reason proceeds from one thing to another. And since the three operations of reason are ordered to each other so are the books: the Praedicamenta to the Perihermeneias and the Perihermeneias to the Priora and the books following it.

             3. The one we are now examining is named Perihermeneias, that is, On Interpretation. Interpretation, according to Boethius, is significant vocal sound--whether complex or incomplex--which signifies something by itself. Conjunctions, then, and prepositions and other words of this kind are not called interpretations since they do not signify anything by themselves. Nor can sounds signifying naturally but not from purpose or in connection with a mental image of signifying something -such as the sounds of brute animals--be called interpretations, for one who interprets intends to explain something. Therefore only names and verbs and speech are called interpretations and these Aristotle treats in this book.

             The name and verb, however, seem to be principles of interpretation rather than interpretations, for one who interprets seems to explain something as either true or false. Therefore, only enunciative speech in which truth or falsity is found is called interpretation. Other kinds of speech, such as optatives and imperatives, are ordered rather to expressing volition than to interpreting what is in the intellect. This book, then, is entitled On Interpretation, that is to say, On Enunciative Speech in which truth or falsity is found. The name and verb are treated only insofar as they are parts of the enunciation; for it is proper to a science to treat the parts of its subject as well as its properties.

             It is clear, then, to which part of philosophy this book belongs, what its necessity is, and what its place is among the books on logic.