Definition: Duration is a property whereby goodness, greatness, power etc. can last.
Distinctions, clarification and exposition: duration has two modes of being: with and without succession. Duration without succession is infinite, it is called eternity from which successive duration arises as a likeness or figure of eternity where the human intellect can apprehend the form of eternity. Thus the form of eternity can actually exist without any time sequence or quantity because the successive kind of duration is not of the essence of eternity just as quantity is not of the essence of infinity. Now this is the eternity of God, namely God Himself and comprises the One who originates, the One who is originated and the Act of originating so that it is not idle, given that nothing is idle in itself and that idleness means cessation of existence and vice versa. It is an actively originating principle, so the goodness, greatness, power etc. of God may not be idle in eternity which is God Himself; this shows that eternity is a substantial being and principle comprising the One who originates, the Act of originating and the One Who is originated; however, this is a transcendent point and difficult for the intellect to reach. The transcendent points will be dealt with further on.
Nature: its innate correlatives are what lasts, what makes it last and their lasting, in one essence of duration that is perfectly full of these simple parts, without which it would have no natural presence.
Obviously, without duration nothing can exist or endure and without duration there is no actuality, being or potentiality; but potentiality has no duration per se as it has no independent existence.
Duration is included in the principles of this Art to show the artist the conditions of eternal duration where the effect is in its cause and vice versa. Hence, the artist must regulate successive duration with eternal duration which is the completely perfect end sought by imperfect, successsive duration.