Concerning what is in our own power, that is, concerning Free-will.

The first enquiry involved in the consideration of free-will, that is, of what is in our own power, is whether anything is in our power, for there are many who deny this.

The second is, what are the things that are in our power, and over what things do we have authority?

The third is, what is the reason for which God Who created us endued us with free-will?

So then we shall take up the first question, and firstly we shall prove that of those things, which even our opponents grant, some are within our power. And let us proceed thus.

St John of Damascus 

An Exposition of the Orthodox Faith