Full Idea
Those thinkers are in error who postulate ...a single matter, for this cannot exist without some 'perceptible contrariety': this Boundless, which they identify with the 'original real', must be either light or heavy, either hot or cold.
Gist of Idea
The Boundless cannot exist on its own, and must have something contrary to it
Source
comment on Anaximander (fragments/reports [c.570 BCE]) by Aristotle - Coming-to-be and Passing-away (Gen/Corr) 329a10
Book Reference
Aristotle: 'The Basic Works of Aristotle', ed/tr. McKeon,Richard [Modern Library Classics 2001], p.508
A Reaction
A dubious objection, I would say. If there has to be a contrasting cold thing to any hot thing, what happens when the cold thing is removed?