viii.), that is (III.
xi.

note), which increases or diminishes, helps or hinders, our power of activity; therefore, that which is entirely different from our nature can neither be to us good nor bad.

Q.E.D.
PROP.XXX.

A thing cannot be bad for us through the quality which it has in common with our nature, but it is bad for us in so far as it is contrary to our nature.
Proof .-- We call a thing bad when it is the cause of pain (IV.
viii.), that is (by the Def., which see in III.xi.

note), when it diminishes or checks our power of action.