[Side-note: Force of the negative case in the Parmenidês. Difficulties about participation of sensible objects in the world of Ideas.] The negative case, made out in the Parmenidês against the theory of Ideas, is indeed most powerful. The hypothesis of the Ideal World is unequivocally affirmed by Sokrates, with its four principal characteristics. 1. Complete essential separation from the world of sense. 2. Absolute self-existence. 3. Plurality of constituent items, several contrary to each other. 4. Unchangeable sameness and unity of each and all of them.--Here we have full satisfaction given to the Platonic sentiment, which often delights in soaring above the world of sense, and sometimes (see Phædon) in heaping contemptuous metaphors upon it. But unfortunately Sokrates cannot disengage himself from this world of sense: he is obliged to maintain that it partakes of, or is determined by, these extra-sensible Forms or Ideas. Here commence the series of difficulties and contradictions brought out by the Elenchus of Parmenides. Are all sensible objects, even such as are vulgar, repulsive, and contemptible, represented in this higher world? The Platonic sentiment shrinks from the admission: the Platonic sense of analogy hesitates to deny it. Then again, how can both assertions be true--first that the two worlds are essentially separate, next, that the one participates in, and derives its essence from, the other? How (to use Aristotelian language[28]) can the essence be separated from that of which it is the essence? How can the Form, essentially One, belong at once to a multitude of particulars? [Footnote 28: Arist. Met. A. 991, b. 1. [Greek: a)du/naton, chôri\s ei)=nai tê\n ou)si/an kai\ ou)= ê( ou)si/a.]] Two points deserve notice in this debate respecting the doctrine of Ideas:-- [Side-note: Difficulties about the Cognizability of Ideas. If Ideas are absolute, they cannot be cognizable: if they are cognizable, they must be relative. Doctrine of Homo Mensura.] 1. Parmenides shows, and Sokrates does not deny, that these Forms or Ideas described as absolute, self-existent, unchangeable, must of necessity be unknown and unknowable to us.[29] Whatever we do know, or can know, is relative to us;--to our actual cognition, or to our cognitive power. If you declare an object to be absolute, you declare it to be neither known nor knowable by us: if it be announced as known or knowable by us, it is thereby implied at the same time not to be absolute. If these Forms or Objects called absolute are known, they can be known only by an absolute Subject, or the Form of a cognizant Subject: that is, by God or the Gods. Even thus, to call them _absolute_ is a misnomer: they are relative to the Subject, and the Subject is relative to them.