To define a genus by its later differentiae rather than its primary ones is no different from evaluating a species by the primary genera instead of the secondary.

The craft of definition is a purely conventional invention, not something innate.

He says: “Observing the proper order in these matters is a condition for perfecting the craft of definition, and it is extremely difficult.”
We reply: This craft is a man-made convention; it is not one of the true scientific realities. Moreover, in a number of instances it flatly contradicts both clear reason and the way things actually exist, and is therefore invalid. It is not a neutral convention like assigning proper names, for the latter is useful and clashes with neither reason nor reality. Their convention, on the other hand, conflicts with both. Even were it a mere convention, it could never serve as a standard for sciences and realities, for genuine scientific facts do not change with changing conventions and terminologies. To know that a thing is living, knowledgeable, capable, willing, moving or at rest, perceptive or imperceptive—this is not a fabricated craft but an objective, innate reality with which God Almighty has endowed His servants, just as He has endowed them with sound desires and upright movements.

All the more surprising is that these people claim that logic is the scale of the rational sciences, and that adhering to it protects the mind from error in thought, just as prosody is the scale of poetry, grammar and morphology the scale of composite and single Arabic expressions, and time-keeping instruments the scales of the hours.

Yet the case is otherwise: rational sciences are learned through the means of cognition God has implanted in the children of Adam; they do not rest upon a conventional scale devised by some individual, nor does one imitate in