its influence and operation. For as like effects necessarily follow
from like causes, and in a contiguous time and place, their
separation for a moment shows that these causes are not complete
ones."--(I. p. 230.)

In addition to the bare notion of necessary connexion between the cause
and its effect, we undoubtedly find in our minds the idea of something
resident in the cause which, as we say, produces the effect, and we call
this something Force, Power, or Energy. Hume explains Force and Power as
the results of the association with inanimate causes of the feelings of
endeavour or resistance which we experience, when our bodies give rise
to, or resist, motion.

If I throw a ball, I have a sense of effort which ends when the ball
leaves my hand; and if I catch a ball, I have a sense of resistance
which comes to an end with the quiescence of the ball. In the former
case, there is a strong suggestion of something having gone from myself
into the ball; in the latter, of something having been received from the
ball. Let any one hold a piece of iron near a strong magnet, and the
feeling that the magnet endeavours to pull the iron one way in the same
manner as he endeavours to pull it in the opposite direction, is very
strong.

As Hume says:--

"No animal can put external bodies in motion without the sentiment
of a _nisus_, or endeavour; and every animal has a sentiment or
feeling from the stroke or blow of an external object that is in
motion. These sensations, which are merely animal, and from which
we can, _a priori_, draw no inference, we are apt to transfer to
inanimate objects, and to suppose that they have some such feelings
whenever they transfer or receive motion."--(IV. p. 91, _note_.)

It is obviously, however, an absurdity not less gross than that of
supposing the sensation of warmth to exist in a fire, to imagine that
the subjective sensation of effort or resistance in ourselves can be
present in external objects, when they stand in the relation of causes
to other objects.

To the argument, that we have a right to suppose the relation of cause
and effect to contain something more than invariable succession,
because, when we ourselves act as causes, or in volition, we are
conscious of exerting power; Hume replies, that we know nothing of the
feeling we call power except as effort or resistance; and that we have
not the slightest means of knowing whether it