There are three kinds: Being, Becoming, and Necessity. The last is introduced by Timaeus, as the level at which the demiurge operates.
The demiurge is not omnipotent, it is the intellect trying to order the chaos.
There is a recalcitrance in the material world, the intellect that designs the perfection of the world did not bring it in; thus, by necessity, there must be something before the activity of the demiurge that moves in all directions, without structure, and resists his influence.
Aristotle
First to intend to write systematic philosophical treatises, elaborating a system of knowledge cover to cover. What we have, however, is not what Aristotle published: there is an enormous problem in sources and how we found him. Much like Plato, Aristotle also wrote dialogues; most of them are entirely lost.
We do, however, have treatises in a large number of scientific disciplines.
Historia animalium describes how a scientific discipline should look like, and how metaphysics encompasses every discipline.
This is what has the scientific method.
But he does not do experiments, does not like mathematics, and disagrees, knowingly, with Darwinism.
To criticize him for a lack of experiments may be anachronistic, to criticize his disavowal of mathematics is not, given his teacher’s (Plato’s) love thereof.
eidos got replaced with morphe