In the Greek tradition, the relationship between time and eternity takes the form of a mysterious passage from the world of perfect and immutable being to its pale copy, the world of becoming in perpetual change. The moving image of eternity for Plato, a consequence of the processual movement of the One for Plotinus, time is often the result of a degradation of the chain of beings that is exhausted in being unfurled. Even though duration is in league with the existence of modes and constitutes the property (propre) of beings that are not self-caused, it does not appear as the indication of an ontological impoverishment in Spinoza. Modes are not the beneficiaries of necessary existence, but they do enjoy a necessity of existing. All things, when conceived sub specie aeternitatis, include, through God's essence, existence – at least if we follow the demonstration of proposition 30 from Ethics V. The eternity of modes is well and truly a reality that is reducible neither to a participation nor to an imperfect imitation. At the same time, through a curious reversal in perspective, it is not the mind's eternity that constitutes a real conundrum, but the appearance and existence of duration. This looks a bit like the mysterious, contingent residue of history of which Hegel speaks, a residue that does not shake the necessity of the process but remains rebellious to it. It is nonetheless clear, to Spinoza's eyes, that the feeling of contingency is the deceptive fruit of a confused understanding and that the existence of duration itself answers to a necessity. Given this situation, it is important to determine why and how eternal modes can endure.

To this end, we must, before anything else, clear away the obstacles that prevent us from understanding the relationship between duration and eternity and that thereby lead to confusion. The first is tied to an apparent difficulty of Spinozist thought which seems to temporalise the intemporal. The second concerns a reworking of the concepts of duration and time in relation to the scholastic tradition. So long as the details of the problem go unclarified, the existence of duration will lead to vain speculations improperly based on the idea of a genesis or a passage from the eternal to the temporal.