The article discusses problem of methodology of The Ancient Natural Science on the material of analysis of the fragment 29cd Timaeus Plato, Comments to this fragment, which were written by Proclus . Particular attention is given to the understanding of science in the philosophy of Plato as "plausible myth", "probable narration", εἰκότα μῦθον. In this regard, consider the concept of "διάνοια", "dianoytic virtue" in the Nicomachean Ethics Aristotle and Aquinas Comments to fragments of Nicomachean Ethics , which states about "dianoytic virtues". Scientific and medical treatises of the great ancient physician Claudius Galen defined as universal standard of scientific knowledge. More detailed we are analysing of the second chapter of the treatise Galen «Περι των Іπποκράτογς και Πλατωνος δογματων», allocated the basic elements of the scientific method of Galen.