King Philip had committed the education of Alexander to Aristotle, and during the Persian campaigns the conqueror contributed materially, not only in money, but otherwise, toward the "Natural History" then in preparation.
The essential principle of the Aristotelian philosophy was, to rise from the study of particulars to a knowledge of general principles or universals, advancing to them by induction.

The induction is the more certain as the facts on which it is based are more numerous; its correctness is established if it should enable us to predict other facts until then unknown.

This system implies endless toil in the collection of facts, both by experiment and observation; it implies also a close meditation on them.

It is, therefore, essentially a method of labor and of reason, not a method of imagination.

The failures that Aristotle himself so often exhibits are no proof of its unreliability, but rather of its trustworthiness.