The word ἀρχή, by which the early cosmologists are usually said to have designated the object of their search, is in this sense purely Aristotelian. It is quite natural that it should be employed in the well-known historical sketch of the First Book of the _Metaphysics_; for Aristotle is there testing the theories of earlier thinkers by his own doctrine of the four causes. But Plato never uses the term in this connexion, and it does not occur once in the genuine fragments of the early philosophers. It is confined to the Stoic and Peripatetic handbooks from which most of our knowledge is derived, and these simply repeat Aristotle. Zeller has pointed out in a footnote[17] that it would be an anachronism to refer the subtle Aristotelian use of the word to the beginnings of speculation. To Anaximander ἀρχή could only have meant “beginning,” and it was far more than a beginning that the early cosmologists were looking for: it was the _eternal_ ground of all things. There is one very important conclusion that follows at once from the account just given of the meaning of φύσις, and it is, that the search for the primary substance really was the thing that interested the Ionian philosophers. Had their main object been, as Teichmüller held it was, the explanation of celestial and meteorological phenomena, their researches would not have been called Περὶ φύσεως ἱστορίη,[18] but rather Περὶ οὐρανοῦ or Περὶ μετεώρων. And this we shall find confirmed by a study of the way in which Greek cosmology developed. The growing thought which may be traced through the successive representatives of any school is always that which concerns the primary substance, while the astronomical and other theories are, in the main, peculiar to the individual thinkers. Teichmüller undoubtedly did good service by his protest against the treatment of these theories as mere isolated curiosities. They form, on the contrary, coherent systems which must be looked at as wholes. But it is none the less true that Greek philosophy began, as it ended, with the search for what was abiding in the flux of things. Footnote 17: Zeller, p. 217, n. 2 (Eng. trans. p. 248, n. 2). See below, Chap. I. p. 57, _n._ 105. Footnote 18: We have the authority of Plato for giving them this name. Cf. _Phd._ 96 a 7, ταύτης τῆς σοφίας ἣν δὴ καλοῦσι περὶ φύσεως ἱστορίαν. So, in the fragment of Euripides referred to on p. 12, _n._ 14, the man who discerns “the ageless order of immortal φύσις” is referred to as ὅστις τῆς ἱστορίας ἔσχε μάθησιν. [Sidenote: Motion and rest.]