P18: Man is affected with the same affect of Joy or Sadness from the image of a past or future thing as from the image of a present thing.

Dem.: So long as a man is affected by the image of a thing, he will regard the thing as present, even if it does not exist (by IIP17 and P17 C); he imagines it as past or future only insofar as its image is joined to the image of a past or future time (see IIP44 S). So the image of a thing, considered only in itself, is the same, whether it is related to time past or future, or to the present, i.e. (by IIP16 C2), the constitution of the Body, or affect, is the same, whether the image is of a thing past or future, or of a present thing. And so, the affect of Joy or Sadness is the same, whether the image is of a thing past or future, or of a present thing, q.e.d.

Schol. I:21 I call a thing past or future here, insofar as we have been affected by it, or will be affected by it. E.g., insofar as we have seen it or will see it, insofar as it has refreshed us or will refresh us, has injured us or will injure us. For insofar as we imagine it in this way, we affirm its existence, i.e., the Body is not affected by any affect that excludes the thing’s existence. And so (by IIP17) the Body is affected with the image of the thing in the same way as if the thing itself were present. However, because it generally happens that those who have experienced many things vacillate so long as they regard a thing as future or past, and most often doubt the thing’s outcome (see IIP44 S), the affects that arise from similar images of things are not so constant, but are generally disturbed by the images of other things, until men become more certain of the thing’s outcome.

Schol. 2: From what has just been said, we understand what Hope and Fear, Confidence and Despair, Gladness and Remorse are. For Hope is nothing but an inconstant Joy which has arisen from the image of a future or past thing whose outcome we doubt; Fear, on the other hand, is an inconstant Sadness, which has also arisen from the image of a doubtful thing. Next, if the doubt involved in these affects is removed, Hope becomes Confidence, and Fear, Despair—viz. a Joy or Sadness which has arisen from the image of a thing we feared or hoped for. Finally, Gladness is a Joy which has arisen from the image of a past thing whose outcome we doubted, while Remorse is a sadness which is opposite to Gladness.