e stars signify rather than cause the things
foretold by means of their observation. But this is an unreasonable
statement: since every corporeal sign is either the effect of that
for which it stands (thus smoke signifies fire whereby it is caused),
or it proceeds from the same cause, so that by signifying the cause,
in consequence it signifies the effect (thus a rainbow is sometimes a
sign of fair weather, in so far as its cause is the cause of fair
weather). Now it cannot be said that the dispositions and movements
of the heavenly bodies are the effect of future events; nor again can
they be ascribed to some common higher cause of a corporeal nature,
although they are referable to a common higher cause, which is divine
providence. On the contrary the appointment of the movements and
positions of the heavenly bodies by divine providence is on a
different principle from the appointment of the occurrence of future
contingencies, because the former are appointed on a principle of
necessity, so that they always occur in the same way, whereas the
latter are appointed on a principle of contingency, so that the
manner of their occurrence is variable. Consequently it is impossible
to acquire foreknowledge of the future from an observation of the
stars, except in so far as effects can be foreknown from their causes.

Now two kinds of effects escape the causality of heavenly bodies. In
the first place all effects that occur accidentally, whether in human
affairs or in the natural order, since, as it is proved in _Metaph._
vi [*Ed. Did. v, 3], an accidental being has no cause, least of all a
natural cause, such as is the power of a heavenly body, because what
occurs accidentally, neither is a _being_ properly speaking, nor is
_one_--for instance, that an earthquake occur when a stone falls, or
that a treasure be discovered when a man digs a grave--for these and
like occurrences are not one thing, but are simply several things.
Whereas the operation of nature has always some one thing for its
term, just as it proceeds from some one principle, which is the form
of a natural thing.

In the second place, acts of the free-will, which is the faculty of
will and reason, escape the causality of heavenly bodies. For the
intellect or reason is not a body, nor the act of a bodily organ, and
consequently neither is the will, since it is in the reason, as the
Philosopher shows (De Anima iii, 4, 9). Now no body can make an
impression on an i