 As if to emphasize that he is speaking not just of the understanding of nature as substance (natura naturans), but also of the passive nature of the existing finite modes (natura naturata), Spinoza cites the troubles one gets into as soon as one attempts to conceive duration through the abstraction of time. The eternity of the attributes and active nature is to be contrasted with the duration of existing modes. Yet to attempt to understand the duration of modes through the abstraction Time, and by implication, to try to understand the spatial extension of modes through Measure and Number, is to employ aids to the imagination only, and inevitably leads not to understanding, but to  absurdities.[17]  We must conclude that Spinoza's views of Measure, Time and Number confound the easy impression that he thought that the variety in matter could be accounted for by motion and rest considered as numerical quantities. Even if we could satisfy Gabbey's demand for a “mathematical account of … proportions of motion and rest and of the measures of motion and rest from which they are formed”, that would not meet Spinoza's own demands for the intellectual understanding of the nature and existence of bodies.