I. The human body can be affected in many ways, whereby
its power of activity is increased or diminished, and also
in other ways which do not render its power of activity
either greater or less.
N.B. This postulate or axiom rests on Postulate i. and
Lemmas v. and vii., which see after II. xiii.
II. The human body can undergo many changes, and,
nevertheless, retain the impressions or traces of objects
(cf. II. Post. v.), and, consequently, the same images
of things (see note II. xvii.).