'Above all we ought at least to know that there are three origins of our thoughts, i.e., from God, from the devil, and from ourselves. . . We ought then carefully to notice this threefold order, and with a wise discretion to analyse the thoughts which arise in our hearts, tracking out their origin and cause and author in the first instance, that we may be able to consider how we ought to yield ourselves to them. . .'
St. Moses the Black Hermit