11.16.21   And yet, Lord, we perceive intervals of times, and compare them, and say, some are shorter, and others longer. We measure also, how much longer or shorter this time is than that; and we answer, "This is double, or treble; and that, but once, or only just so much as that." But we measure times as they are passing, by perceiving them; but past, which now are not, or the future, which are not yet, who can measure? unless a man shall presume to say, that can be measured, which is not. When then time is passing, it may be perceived and measured; but when it is past, it cannot, because it is not.