P21: The Mind can neither imagine anything, nor recollect past things, except while the Body endures.

Dem.: The Mind neither expresses the actual existence of its Body, nor conceives the Body’s affections as actual, except while the Body endures (by IIP8 C); consequently (by IIP26), it conceives no body as actually existing except while its body endures.

Therefore, it can neither imagine anything (see the Def. of Imagination in IIP17 S) nor recollect past things (see the Def. of Memory in IIP18 S) except while the body endures, q.e.d.