along with possession, to act, and to be acted upon. Some made them five, others reduced them to three. A mnemonic verse runs:

Zayd—the tall, the black, son of Mālik—
Yesterday, within his house, lay reclining;
In his hand a sword he drew, and it was drawn—
Thus are ten categories, besides the subject itself.

Thereafter they set about discussing the various species contained in these genera until they reached the first principles of their particular sciences: magnitude, which is the subject of geometry; number, the subject of arithmetic; body, the subject of natural philosophy; and the like. Their remarks on cause and effect, however, were meager.

As for the terminology of “Necessary Existent” and “Possible Existent,” this belongs to Ibn Sīnā and his peers, who borrowed it from the Muʿtazilite theologians and the like. In the writings of their predecessors one finds only the language of cause and caused.

I have dealt elsewhere with what their first teacher, Aristotle, said on these matters, showing how little sound benefit it contains, how often it falls short, and how rife it is with error—truly, as the saying goes,

“Lean camel meat perched atop a rugged mountain:
Too steep to scale, too scant to roast.”

Those men sought to prove the First Cause on the basis that the celestial sphere moves by volition, and whatever moves by volition must have an object of desire that sets it in motion, just as the beloved stirs the lover. Even if that were granted, it would establish only that the sphere has a final cause; it would not show that it is itself an effect.