It was thus from Xenophanes that the doctrine of Pankosmism obtained introduction into Greek philosophy, recognising nothing real except the universe as an indivisible and unchangeable whole. Such a creed was altogether at variance with common perception, which apprehends the universe as a plurality of substances, distinguishable, divisible, changeable, &c. And Xenophanes could not represent his One and All, which excluded all change, to be the substratum out of which phenomenal variety was generated--as Water, Air, the Infinite, had been represented by the Ionic philosophers. The sense of this contradiction, without knowing how to resolve it, appears to have occasioned the mournful complaints of irremediable doubt and uncertainty, preserved as fragments from his poems. "No man (he exclaims) knows clearly about the Gods or the universe: even if he speak what is perfectly true, he himself does not know it to be true: all is matter of opinion."[54] [Footnote 54: Xenophan. Fragm. 14, p. 51, ed. Karsten. [Greek: kai\ to\ me\n ou)=n saphe\s ou)/tis a)nê\r ge/net' ou)/de tis e)/stai ei)dô\s, a)mphi\ theô=n te kai\ a)/ssa le/gô peri\ pa/ntôn; ei) ga\r kai\ ta\ ma/lista tu/choi tetelesme/non ei)pô\n, au)to\s o(mô=s ou)k oi)=de; do/kos d' e)pi\ pa=si te/tuktai]. Compare the extract from the Silli of Timon in Sextus Empiricus--Pyrrhon. Hypot. i. 224; and the same author, adv. Mathemat. vii. 48-52.] Nevertheless while denying all real variety or division in the universe, Xenophanes did not deny the variety of human perceptions and beliefs. But he allowed them as facts belonging to man, not to the universe--as subjective or relative, not as objective or absolute. He even promulgated opinions of his own respecting many of the physical and cosmological subjects treated by the Ionic philosophers. [Side-note: His conjectures on physics and astronomy.] Without attempting to define the figure of the Earth, he considered it to be of vast extent and of infinite depth;[55] including, in its interior cavities, prodigious reservoirs both of fire and water. He thought that it had at one time been covered with water, in proof of which he noticed the numerous shells found inland and on mountain tops, together with the prints of various fish which he had observed in the quarries of Syracuse, in the island of Paros, and elsewhere. From these facts he inferred that the earth had once been covered with water, and even that it would again be so covered at some future time, to the destruction of animal and human life.[56] He supposed that the sun, moon, and stars were condensations of vapours exhaled from the Earth, collected into clouds, and alternately inflamed and extinguished.[57] [Footnote 55: Aristot. De Coelo, ii. 13.] [Footnote 56: Xenophan. Fragm. p. 178, ed. Karsten; Achilles Tatius, [Greek: Ei)sagôgê\] in Arat. Phænom. p. 128, [Greek: ta\ ka/tô d' e)s a)/peiron i(ka/nei].