ecessary for the three angles of a
triangle to be equal to two right angles. And this is "natural" and
"absolute necessity." In another way, that a thing must be, belongs
to it by reason of something extrinsic, which is either the end or
the agent. On the part of the end, as when without it the end is not
to be attained or so well attained: for instance, food is said to be
necessary for life, and a horse is necessary for a journey. This is
called "necessity of end," and sometimes also "utility." On the part
of the agent, a thing must be, when someone is forced by some agent,
so that he is not able to do the contrary. This is called "necessity
of coercion."

Now this necessity of coercion is altogether repugnant to the will.
For we call that violent which is against the inclination of a thing.
But the very movement of the will is an inclination to something.
Therefore, as a thing is called natural because it is according to the
inclination of nature, so a thing is called voluntary because it is
according to the inclination of the will. Therefore, just as it is
impossible for a thing to be at the same time violent and natural, so
it is impossible for a thing to be absolutely coerced or violent, and
voluntary.

But necessity of end is not repugnant to the will, when the end cannot
be attained except in one way: thus from the will to cross the sea,
arises in the will the necessity to wish for a ship.

In like manner neither is natural necessity repugnant to the will.
Indeed, more than this, for as the intellect of necessity adheres to
the first principles, the will must of necessity adhere to the last
end, which is happiness: since the end is in practical matters what
the principle is in speculative matters. For what befits a thing
naturally and immovably must be the root and principle of all else
appertaining thereto, since the nature of a thing is the first in
everything, and every movement arises from something immovable.

Reply Obj. 1: The words of Augustine are to be understood of the
necessity of coercion. But natural necessity "does not take away
the liberty of the will," as he says himself (De Civ. Dei v, 10).

Reply Obj. 2: The will, so far as it desires a thing naturally,
corresponds rather to the intellect as regards natural principles
than to the reason, which extends to opposite things. Wherefore in
this respect it is rather an intellectual than a rational power.

Reply Obj. 3: We are masters of our own