Full Idea
Aristotle, and also the Stoics, denied rationality to animals. …The Platonists, the Pythagoreans, and some more independent Aristotelians, did grant reason and intellect to animals.
Gist of Idea
Aristotle and the Stoics denied rationality to animals, while Platonists affirmed it
Source
report of Aristotle (works [c.330 BCE]) by Richard Sorabji - Rationality 'Denial'
Book Reference
'Rationality in Greek Thought', ed/tr. Frede,M /Striker,G [OUP 1999], p.311
A Reaction
This is not the same as affirming or denying their consciousness. The debate depends on how rationality is conceived.