them by their nature. Of this kind are plants, which move
themselves according to their inherent nature, with regard only to
executing the movements of growth and decay.

Other things have self-movement in a higher degree, that is, not only
with regard to executing the movement, but even as regards to the
form, the principle of movement, which form they acquire of
themselves. Of this kind are animals, in which the principle of
movement is not a naturally implanted form; but one received through
sense. Hence the more perfect is their sense, the more perfect is
their power of self-movement. Such as have only the sense of touch, as
shellfish, move only with the motion of expansion and contraction; and
thus their movement hardly exceeds that of plants. Whereas such as
have the sensitive power in perfection, so as to recognize not only
connection and touch, but also objects apart from themselves, can move
themselves to a distance by progressive movement. Yet although animals
of the latter kind receive through sense the form that is the
principle of their movement, nevertheless they cannot of themselves
propose to themselves the end of their operation, or movement; for
this has been implanted in them by nature; and by natural instinct
they are moved to any action through the form apprehended by sense.
Hence such animals as move themselves in respect to an end they
themselves propose are superior to these. This can only be done by
reason and intellect; whose province it is to know the proportion
between the end and the means to that end, and duly coordinate them.
Hence a more perfect degree of life is that of intelligent beings;
for their power of self-movement is more perfect. This is shown by the
fact that in one and the same man the intellectual faculty moves the
sensitive powers; and these by their command move the organs of
movement. Thus in the arts we see that the art of using a ship, i.e.
the art of navigation, rules the art of ship-designing; and this in
its turn rules the art that is only concerned with preparing the
material for the ship.

But although our intellect moves itself to some things, yet others are
supplied by nature, as are first principles, which it cannot doubt;
and the last end, which it cannot but will. Hence, although with
respect to some things it moves itself, yet with regard to other
things it must be moved by another. Wherefore that being whose act of
understanding is its very nature, and whi