into two-legged creatures and many-legged ones, for an animal is not predisposed to having two or several legs merely by virtue of being an animal, but rather by virtue of being a walker; and it becomes capable of walking insofar as it is an animal.

Thus, observing the proper order in these matters is a prerequisite for fulfilling the craft of definition, and it is exceedingly arduous. Because of this difficulty, the theologians contented themselves with mere differentiation, declaring that a definition is no more than “a statement that gathers what belongs under it and bars what does not,” requiring of it nothing beyond distinctiveness.

This position necessarily allows one to settle for accidental properties, so that a horse would be defined as “the neighing creature,” a human being as “the laughing one,” and a dog as “the barking one”—all of which stand far from the purpose of defining the very essence of the thing defined.

Owing to the hardship of precise definition, we have decided to present a set of well-known, carefully edited definitions in the second section of the Book of Definitions.

He then said:

Section Two
On Detailed Definitions

Know that the things capable of being defined are without limit, for demonstrative sciences are infinite and depend upon conceptions, and the least a proposition contains is two conceptions. In sum, everything that has a name can have its essential definition, its descriptive outline, or at least an explanation of its name. Since exhaustive coverage is unattainable, it is better to confine ourselves to the established rules of the discipline, which have been supplied in the first section.

Nevertheless, we have set down detailed definitions for two benefits:

First, to acquire practical skill in composing and formulating definitions, for repeated testing and practice inevitably strengthen one’s command over a matter.

Second, to gain insight into the meanings of terms employed by the philosophers. We cited them in The Incoherence of the Philosophers, for they can only be debated in their own language and according to their conventions; if we fail to understand the terminology we have transmitted from them, disputing with them becomes impossible.