Again, the new position occupied by Mind as an intermediary between the world of reality and the world of appearance, tended more and more to obliterate or confuse the demarcations by which they had hitherto been separated. The most general headings under which it was usual to contrast them were, the One and the Many, Being and Nothing, the Same and the Different, Rest and Motion. Parmenides employed the one set of terms to describe his Absolute, and the other to describe the objects of vulgar belief. They also served respectively to designate the wise and the ignorant, the dialectician and the sophist, the knowledge of gods and the opinions of men; besides offering points of contact with the antithetical couples of Pythagoreanism. But Plato gradually found that the nature of Mind could not be understood without taking both points of view into account. Unity and plurality, sameness and difference, equally entered into its composition; although undoubtedly belonging to the sphere of reality, it was self-moved and the cause of all motion in other things. The dialectic or classificatory method, with its progressive series of differentiations and assimilations, also involved a continual use of categories which were held to be mutually exclusive. And on proceeding to an examination of the summa genera, the highest and most abstract ideas which it had been sought to distinguish by their absolute purity and simplicity from the shifting chaos of sensible phenomena, Plato discovered that even these were reduced to a maze of confusion and contradiction by a sincere application of the cross-examining elenchus. For example, to predicate being of the One was to mix it up with a heterogeneous idea and let in the very plurality which it denied. To distinguish them was to predicate difference of both, and thus open the door to fresh embarrassments.