Diogenes Laertius Vitae philosophorum 1.prol.21

[21] One word more: not long ago an Eclectic school was introduced by Potamo of Alexandria, ¹ , who made a selection from the tenets of all the existing sects. As he himself states in his Elements of Philosophy, he takes as criteria of truth (1) that by which the judgement is formed, namely, the ruling principle of the soul; (2) the instrument used, for instance the most accurate perception. His universal principles are matter and the efficient cause, quality, and place; for that out of which and that by which a thing is made, as well as the quality with which and the place in which it is made, are principles. The end to which he refers all actions is life made perfect in all virtue, natural advantages of body and environment being indispensable to its attainment.

It remains to speak of the philosophers themselves, and in the first place of Thales.