The Complete Aristotle (eng.)

their fellows are trodden under foot. Even these
things, however, can in a way be affected by chance, when one who
is dealing with them does something to them by chance, but not
otherwise.
    The spontaneous on the other hand is found both in the lower
animals and in many inanimate objects. We say, for example, that
the horse came ‘spontaneously’, because, though his coming saved
him, he did not come for the sake of safety. Again, the tripod fell
‘of itself’, because, though when it fell it stood on its feet so
as to serve for a seat, it did not fall for the sake of that.
    Hence it is clear that events which (1) belong to the general
class of things that may come to pass for the sake of something,
(2) do not come to pass for the sake of what actually results, and
(3) have an external cause, may be described by the phrase ‘from
spontaneity’. These ‘spontaneous’ events are said to be ‘from
chance’ if they have the further characteristics of being the
objects of deliberate intention and due to agents capable of that
mode of action. This is indicated by the phrase ‘in vain’, which is
used when A which is for the sake of B, does not result in B. For
instance, taking a walk is for the sake of evacuation of the
bowels; if this does not follow after walking, we say that we have
walked ‘in vain’ and that the walking was ‘vain’. This implies that
what is naturally the means to an end is ‘in vain’, when it does
not effect the end towards which it was the natural means-for it
would be absurd for a man to say that he had bathed in vain because
the sun was not eclipsed, since the one was not done with a view to
the other. Thus the spontaneous is even according to its derivation
the case in which the thing itself happens in vain. The stone that
struck the man did not fall for the purpose of striking him;
therefore it fell spontaneously, because it might have fallen by
the action of an agent and for the purpose of striking. The
difference between spontaneity and what results by chance is
greatest in things that come to be by nature; for when anything
comes to be contrary to nature, we do not say that it came to be by
chance, but by spontaneity. Yet strictly this too is different from
the spontaneous proper; for the cause of the latter is external,
that of the former internal.
    We have now explained what chance is and what spontaneity is,
and in what they differ from each other. Both belong to the mode of
causation ‘source of change’, for either some natural or some
intelligent agent is always the cause; but in this sort of
causation the number of possible causes is infinite.
    Spontaneity and chance are causes of effects which though they
might result from intelligence or nature, have in fact been caused
by something incidentally. Now since nothing which is incidental is
prior to what is per se, it is clear that no incidental cause can
be prior to a cause per se. Spontaneity and chance, therefore, are
posterior to intelligence and nature. Hence, however true it may be
that the heavens are due to spontaneity, it will still be true that
intelligence and nature will be prior causes of this All and of
many things in it besides.
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7
    It is clear then that there are causes, and that the number of
them is what we have stated. The number is the same as that of the
things comprehended under the question ‘why’. The ‘why’ is referred
ultimately either (1), in things which do not involve motion, e.g.
in mathematics, to the ‘what’ (to the definition of ‘straight line’
or ‘commensurable’, &c.), or (2) to what initiated a motion,
e.g. ‘why did they go to war?-because there had been a raid’; or
(3) we are inquiring ‘for the sake of what?’-’that they may rule’;
or (4), in the case of things that come into being, we are looking
for the matter. The causes, therefore, are these and so many in
number.
    Now, the causes being four, it is the business of the physicist
to know about them all, and if he refers his problems back to all
of them, he will assign the ‘why’ in the way proper to his
science-the matter, the form, the mover, ‘that for the sake of
which’. The last three often coincide; for the ‘what’ and ‘that for
the sake of which’ are one, while the primary source of motion is
the same in species as these (for man generates man), and so too,
in general, are all things which cause movement by being themselves
moved; and