in movement, and a
desire that that movement should take place; if I will to think of any
subject, or, in other words, to attend to that subject, I have an idea
of the subject and a strong desire that it should remain present to my
consciousness. And so far as I can discover, this combination of an idea
of an object with an emotion, is everything that can be directly
observed in an act of volition. So that Hume's definition may be amended
thus: Volition is the impression which arises when the idea of a bodily
or mental action is accompanied by the desire that the action should be
accomplished. It differs from other desires simply in the fact, that we
regard ourselves as possible causes of the action desired.

Two questions arise, in connexion with the observation of the phenomenon
of volition, as they arise out of the contemplation of all other natural
phenomena. Firstly, has it a cause; and, if so, what is its cause?
Secondly, is it followed by any effect, and if so, what effect does it
produce?

Hume points out, that the nature of the phenomena we consider can have
nothing to do with the origin of the conception that they are connected
by the relation of cause and effect. For that relation is nothing but an
order of succession, which, so far as our experience goes, is
invariable; and it is obvious that the nature of phenomena has nothing
to do with their order. Whatever it is that leads us to seek for a cause
for every event, in the case of the phenomena of the external world,
compels us, with equal cogency, to seek it in that of the mind.

The only meaning of the law of causation, in the physical world, is,
that it generalises universal experience of the order of that world;
and, if experience shows a similar order to obtain among states of
consciousness, the law of causation will properly express that order.

That such an order exists, however, is acknowledged by every sane man:

"Our idea, therefore, of necessity and causation, arises entirely
from the uniformity observable in the operations of nature, where
similar objects are constantly conjoined together, and the mind is
determined by custom to infer the one from the appearance of the
other. These two circumstances form the whole of that necessity
which we ascribe to matter. Beyond the constant _conjunction_ of
similar objects and the consequent _inference_ from one to the
other, we have no notion of any necessity of c