P28: We strive to further the occurrence of whatever we imagine will lead to Joy, and to avert or destroy what we imagine is contrary to it, or will lead to Sadness.

Dem.: We strive to imagine, as far as we can, what we imagine will lead to Joy (by P12), i.e. (by IIP17), we strive, as far as we can, to regard it as present, or as actually existing.

But the Mind’s striving, or power of thinking, is equal to and at one in nature with the Body’s striving, or power of acting (as clearly follows from IIP7 C and P11 C). Therefore, we strive absolutely, or (what, by P9 S, is the same) want and intend that it should exist. This was the first point.

Next, if we imagine that what we believe to be the cause of Sadness, i.e. (by P13 S), what we hate, is destroyed, we shall rejoice (by P20), and so (by the first part of this {NS: proposition}) we shall strive to destroy it, or (by P13) to avert it from ourselves, so that we shall not regard it as present. This was the second point. Therefore, {we strive to further the occurrence of} whatever we imagine will lead to Joy, etc., q.e.d.