Prologue — Prologue

A small error at the outset can lead to great errors in the final conclusions, as the Philosopher says in de Caelo et mundo 1.5, (Aristotle, de Caelo et mundo, 271b8–13.) and thus, since being and essence are the things first conceived of by the intellect, as Avicenna says at the beginning of his Metaphysics 1.6, in order to avoid errors arising from ignorance about these two things, we should make plain the difficulties surrounding them by explaining what the terms being and essence each signify and by showing how each may be found in various things and how each is related to the logical intentions of genus, species, and difference.

Since we ought to acquire knowledge of simple things from composite ones and come to know what is prior from what is posterior, we advance in learning more readily when we begin with what is easier, and thus we should first consider the signification of being and then proceed from there to the signification of essence.