Full Idea
In an irrational being the appetite for what gives it pleasure is insatiable and indiscriminate, and the exercise of the desire increases its innate tendency; and if these appetites are strong and violent, they actually drive out reason.
Gist of Idea
If beings are dominated by appetite, this can increase so much that it drives out reason
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1119b09)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.141
A Reaction
The end-result of this would be a person Aristotle describes as 'brutish'. The remark seems significant because, even though man is essentially a 'rational animal' (man's 'proper function'), it is actually possible to annihilate our reason.