A man acting instinctively may be acting quite reasonably, in a way which any one fully conscious of all the implications and consequences of the action would judge to be reasonable.

But in order that his actions should be free he must himself be fully conscious of all those implications and consequences.
It follows that the end of mankind upon earth is to reach a state in which all the relations of life shall be ordered according to reason, not instinctively but with full consciousness and deliberate purpose.
This end should govern the ethical rules of conduct, and it determines the necessary stages of history.
It gives us at once two main periods, the earliest and the latest: the earliest, in which men act reasonably by instinct, and the latest, in which they are conscious of reason and try to realise it fully.

But before reaching this final stage they must pass through an epoch in which reason is conscious of itself, but not regnant.

And to reach this they must have emancipated themselves from instinct, and this process of emancipation means a fourth epoch.

But they could not have wanted to emancipate themselves unless they had felt instinct as a servitude imposed by an external authority, and therefore we have to distinguish yet another epoch wherein reason is expressed in authoritarian institutions to which men blindly submit.