It is in you, O my mind, that I measure time. Do not interrrupt me by clamoring that time has objective existence! I measure time in you. The impression which things cause in you as they pass by remains even when they are gone. This, which is still present, is what I measure, not those things which have passed by to make this impression. This is what I measure when I measure time. Either, then, this is time, or I do not measure time. (254)
The measurement of time, therefore, is due to our mental capacities for considering, remembering, and expecting in such a way that "what it expects, through what it considers, passes into what it remembers" (254).
Augustine's solution seems to make time something mental. Despite any of the apparent objectsion ("Do not interrupt me by clamoring that time has objective existence!"), there is a certain sophistication to the theory: time is simply a particular way in which we regard changing things. It has the advantage that under it we are not tempted to reify time; and it has the added advantage of fitting especially well with all those of our intuitions that treat time as a measure. If time is a measuring out of entities, however, and that measurment is accomplished entirely by the different attitudes of the mind, time is something mental precisely insofar as it is a measure.