plain the world without introducing the notion of purpose or final cause. The "final cause" of an
occurrence is an event in the future for the sake of which the occurrence takes place. In human
affairs, this conception is applicable. Why does the baker make bread? Because people will be
hungry. Why are railways built? Because people will wish to travel. In such cases, things are
explained by the purpose they serve. When we ask "why?" concerning an event, we may mean
either of two things. We may mean: "What purpose did this event serve?" or we may mean: "What
earlier circumstances caused this event?" The answer to the former question is a teleological
explanation, or an explanation by final causes; the answer to the latter question is a mechanistic
explanation. I do not see how it could have been known in advance which of these two questions
science ought to ask, or whether it ought to ask both. But experience has shown that the
mechanistic question leads to scientific knowledge, while the teleological question does not. The
atomists asked the mechanistic question, and gave a mechanistic answer. Their successors, until
the Renaissance, were more interested in the teleological question, and thus led science up a blind
alley.
In regard to both questions alike, there is a limitation which is often ignored, both in popular
thought and in philosophy. Neither question can be asked intelligibly about reality as a whole
(including God), but only about parts of it. As regards the teleological explanation, it usually
arrives, before long, at a Creator, or at least an Artificer, whose purposes are realized in the course
of nature. But if a man is so obstinately teleological as to continue to ask what purpose is served
by the Creator, it becomes obvious that his question is impious. It is, moreover, unmeaning, since,
to make it significant, we should have to suppose the Creator created by some super-Creator
whose purposes He served. The conception of purpose, therefore, is only applicable within reality,
not to reality as a whole.
A not dissimilar argument applies to mechanistic explanations. One event is caused by another,
the other by a third, and so on. But if we ask for a cause of the whole, we are driven again to the
Creator, who must Himself be uncaused. All causal explanations, therefore, must have an arbitrary
beginning. That is why it is no defect in the theory of the atomists to have left the original
movements of the atoms unaccounted for.