Chapter 26. Events, both under our control and not. (Book 2. The created world, and man's faculties and potential) (On the Orthodox Faith) (Damascene, John)

Of events, some are in our hands, others are not. Those then are in our hands which we are free to do or not to do at our will, that is all actions that are done voluntarily (for those actions are not called voluntary the doing of which is not in our hands), and in a word, all that are followed by blame or praise and depend on motive and law. Strictly all mental and deliberative acts are in our hands. Now deliberation is concerned with equal possibilities: and an 'equal possibility' is an action that is itself within our power and its opposite, and our mind makes choice of the alternatives, and this is the origin of action. The actions, therefore, that are in our hands are these equal possibilities: e.g., to be moved or not to be moved, to hasten or not to hasten, to long for unnecessaries or not to do so, to tell lies or not to tell lies, to give or not to give, to rejoice or not to rejoice as fits the occasion, and all such actions as imply virtue or vice in their performance, for we are free to do or not to do these at our pleasure. Amongst equal possibilities also are included the arts, for we have it in our power to cultivate these or not as we please.

Note, however, that while the choice of what is to be done is ever in our power, the action itself often is prevented by some dispensation of the divine Providence.