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xliv PREFACE lated ratio rather than by some accredited English term, as, for example: notion, concept, idea, rationale, principle, etc. The ratio of genus, species and difference is in effect a reference in intentions; nor would one speak of the notion, rationale, etc. of 2 : 4. An essence in one sense may be compared to a set of ratios and thus like an equation in mathematics has a typical form. The rough draft of this translation was first made for my own use in 1934-1935 during my academic year at Yale Uni- versity as the Sterling Fellow in philosophy^ consequently, I wish to acknowledge the opportunity which the fellowship afforded me. To Dr. Lewis M. Hammond, with whom the translation of the first part of the opusculum was begun, I owe a debt of initiation. For her assistance throughout with the burden of translation, and especially for her precise insights as to modes of rendition, a special measure of appreciation is due to my wife. Professor Scott Buchanan has contributed much to my appreciation of Greek and Scholastic methods, but I should be pained to suppose that any errors of mine might be attributed to anyone except myself. GEORGE G. LECKIE. Amherst Court House, Virginia. CONCERNING BEING AND ESSENCE CONCERNING BEING AND ESSENCE INTRODUCTION "BECAUSE a small error in the beginning is a great one in the -*-* end, according to the Philosopher in the first book of the De Caelo et Mundo? and since being and essence are what are first conceived by the intellect, as Avicenna says in the first book of his Metaphysics, 2 therefore, lest error befall from ig- norance of them (being and essence), in order to reveal their difficulty it should be said what is signified by the names being and essence, and how they are found in diverse things and how they are disposed with respect to (se habeant ad) logical intentions, namely, genus, species, and difference. 1 Aristotle, De Caelo et Mundo, A, 271 b 8-13. 2 Avicenna, Metaphysics, Tr. I, Cap. 6, f. 72 b A.