Form is lacking to water as conceived by Thales. How is this accorded to it? The method is stated (and stated by Aristotle, but not directly of Thales), in which particular forms have arisen out of water; it is said to be through a process of condensation and rarefaction (_πυκνότητι καὶ μανότητι_), or, as it may be better put, through greater or less intensity. Tennemann (vol. I. p. 59) in reference to this, cites from Aristotle, _De gen. et corrupt._ I. 1, where there is no mention of condensation and rarefaction as regards Thales, and further, _De cælo_, III. 5, where it is only said that those who uphold water or air, or something finer than water or coarser than air, define difference as density and rarity, but nothing is said of its being Thales who gave expression to this distinction. Tiedmann (vol. I. p. 38) quotes yet other authorities; it was, however, later on, that this distinction was first ascribed to Thales.[22] Thus much is made out, that for the first time in this natural philosophy as in the modern, that which is essential in form is really the quantitative difference in its existence. This merely quantitative difference, however, which, as the increasing and decreasing density of water, constitutes its only form-determination, is an external expression of the absolute difference; it is an unessential distinction set up through another and is not the inner difference of the Notion in itself; it is therefore not worth while to spend more time over it. Difference as regards the Notion has no physical significance, but differences or the simple duality of form in the sides of its opposition, must be comprehended as universally in the Notion. On this account a sensuous interpretation must not be given to the material, that is to particular determinations, as when it is definitely said that rare water is air, rare air, fiery ether, thick water, mud, which then becomes earth; according to this, air would be the rarefaction of the first water, ether the rarefaction of air, and earth and mud the sediment of water. As sensuous difference or change, the division here appears as something manifested for consciousness; the moderns have experimented in making thicker and thinner what to the senses is the same.