By reason he reflects upon the past, and judges what may happen in the future. He sees the consequences of his actions. He not only knows what he does, but why he does it. Brute animals have not reason, but only instinct, i.e., they follow certain impulses or feelings which God gave them at their creation. If animals could reason, they ought to improve in their condition.
Men become more civilized day by day.
They invent many things that were unknown to their forefathers. One man can improve upon the works of another, etc. But, we never see anything of this kind in the actions of animals. The same kind of birds, for instance, build the same kind of nests, generation after generation, without ever making change or improvement in them. When man teaches an animal any action, it cannot teach the same to its young.