‘Abd al-Latif reminds that in Aristotle’s science of nature the fundamental epistemological criterion holds that man must start from what is attested to by the senses, to then proceed to what is hidden, until he knows everything which he desires to know. For this reason, he goes on in the study of plants and then of animals. He catalogues their species, and explains the apparatus of organs which each animal species is provided with. Since organs alone are not sufficient to explain animal life, man feels the need to introduce a further principle, which is the soul. Nevertheless, the soul is not a principle sufficient to explain man, since the actions of man reveal themselves to be more powerful than the acts of the soul. The soul is not enough to explain the highest degree of substantiality reached by man: Aristotle found man with speech and speech proceeds from intellect or the intellectual principles and powers.