Q.E.D.
PROP.III.

The force whereby a man persists in existing is limited, and is infinitely surpassed by the power of external causes.
Proof .-- This is evident from the axiom of this part.

For, when man is given, there is something else--say A--more powerful; when A is given, there is something else--say B--more powerful than A, and so on to infinity; thus the power of man is limited by the power of some other thing, and is infinitely surpassed by the power of external causes.

Q.E.D.
PROP.IV.

It is impossible, that man should not be a part of Nature, or that he should be capable of undergoing no changes, save such as can be understood through his nature only as their adequate cause.
Proof .-- The power, whereby each particular thing, and consequently man, preserves his being, is the power of God or of Nature (I.xxiv.