 For Avempace, the main purpose of the Eisagoge is to explain the concepts that underlie the ten Aristotelian categories. The first interpretation of “that which is by its nature” is more appropriate to this purpose because the second interpretation affects all beings, but the categories do not affect all beings and they deal with existents insofar as the mind acquires them. These concepts are of two kinds: simple and composite. The simple ones are the five universals and the three composite are the definition, the description and the aforementioned “restricted composition”.