Eighth
If a definition is nothing more than the utterance of the definer, it is self-evident that conceiving meanings does not depend on words. A speaker can grasp the meaning of what he wishes to say without first clothing it in language, and a listener may form a conception of those meanings even when no one addresses him at all. How, then, can it be claimed that individual concepts cannot be grasped except through a definition, which is nothing but the definer’s statement?
Ninth
The things we apprehend are either perceived by our outward senses—such as taste, color, smell, and the bodies that possess those qualities—or by our inward faculties, as with experiential inner states like hunger and satiety, love and hatred, joy and sorrow, pleasure and pain, will and aversion, knowledge and ignorance, and the like. Each of these may be conceived as a particular instance or in an unrestricted, general way. All such conceptions are independent of formal definitions, for a person cannot perceive anything except through his outward and inward faculties; whatever lies beyond his direct perception he comes to know by reasoning and drawing analogies with what he has experienced.
Tenth
They further state that an objector may challenge the definer’s definition through refutation (naqḍ) or counter-argument (muʿāraḍah).
Refutation has two aspects: forward entailment (ṭard) and converse entailment (ʿaks). Forward entailment requires that wherever the definition applies, the thing defined must also be found; the definition thus excludes everything else. Should one demonstrate a case in which the definition applies yet the definiendum is absent, the definition is neither uniform nor exclusive, for it has admitted something other than the intended subject—such as defining “human being” merely as “animal.”
Converse entailment demands that wherever the definition is absent, the thing defined must likewise be absent, making the definition exhaustive. If it is not exhaustive, the definition may be absent while some instances of the definiendum persist—as in defining “human being” as “Arab,” which clearly fails in the converse direction. One might even use the term “forward entailment” where “converse” is intended without causing confusion; the point is that definition and definiendum must correspond exactly in scope. The definition must match the thing defined, admitting nothing extraneous and omitting nothing essential. Whenever one is broader than the other, the definition is unanimously deemed invalid, and this invalidity is what they call naqḍ (refutation).