various places—is that much knowledge is self-evident and innate. When someone seeks to establish it through argument, it becomes obscure and subject to doubt, either because the argument involves a lengthy sequence of premises, because those premises are obscure, or because of both.

The person presenting the argument may be unable to formulate a proof, either because he cannot conceive it or because he cannot express it. For not everyone can put into words everything that a person can conceive. The listener, in turn, may be unable to understand that proof. Even when the proof can be formulated and understood, either the person presenting it, the listener, or both may be unable to dispel the objections raised against it.

[Ibn Taymiyya’s discussion of conceptions]

This occurs more often with conceptions than with judgments. Many well-known matters, when defined by definitions that draw distinctions between them and the things defined, become obscure after having been clear, because they are more evident to the intellect without such a definition than with it.

[The nature of definitions]

Nevertheless, proofs and definitions may offer benefits to which attention has been drawn more than once. Hence people have adopted diverse approaches to definitions and proofs. You will find many people criticizing others’ definitions and proofs, only to present definitions and proofs of their own that admit objections of the same kind, or of another kind.

For the purpose of definitions is as follows:

If the aim is to distinguish the thing defined from everything else, then definitions that include all instances of the thing defined and exclude everything else, whatever their form, all achieve this distinction. If they do not meet these conditions, they all fail to achieve it. If, however, the aim is to impart knowledge of the thing defined, this is not invariably achieved through definitions, nor is it precluded by them