In the fourth book of the Metaphysica, Aristotle gives an explanation of _Ad Aliquid_ different from, and superior to, that which we read in the Categoriæ; treating it, not as one among many distinct Categories, but as implicated with all the Categories, and taking a different character according as it is blended with one or the other--_Essentia_, _Quantum_, _Quale_, _Actio_, _Passio_, &c.[102] He there, also, enumerates as one of the varieties of _Relata_, what seems to go beyond the limit, or at least beyond the direct denotation, of the Categories; for, having specified, as one variety, _Relata Numero_, and, as another, _Relata secundum actionem et passionem ([Greek: to\ thermantiko\n pro\s to\ thermanto/n], &c.), he proceeds to a third variety, such as the _mensurabile_ with reference to _mensura_, the _scibile_ with reference to _scientia_, the _cogitabile_ with reference to _cogitatio_; and in regard to this third variety, he draws a nice distinction. He says that _mensura_ and _cogitatio_ are _Ad Aliquid_, not because they are themselves related to _mensurabile_ and _cogitabile_, but because _mensurabile_ and _cogitabile_ are related to them.[103] You cannot say (he thinks) that mensura is referable to the _mensurabile_, or _cogitatio_ to the _cogitabile_, because that would be repeating the same word twice over--_mensura est illius cujus est mensura_--_cogitatio est illius cujus est cogitatio._ So that he regards _mensura_ and _cogitatio_ as _Correlata_, rather than as _Relata_; while _mensurabile_ and _cogitabile_ are the _Relata_ to them. But in point of fact, the distinction is not important; of the relative pair there may be one which is more properly called the _Correlatum_; yet both are alike relative. [Footnote 102: Metaphys. [Greek: D]. p. 1020, b. 27-32. At the same time we must remark, that while Aristotle enumerates [Greek: to\ u(pe/rechon] and [Greek: to\ u(perecho/menon] under [Greek: Pro/s ti], he had just before (a. 25) ranked [Greek: to\ me/ga kai\ to\ mikro/n, to\ mei=zon kai\ to\ e(/latton], under the general head [Greek: Poso/n]--as [Greek: posou= pa/thê kath' au(ta/].]