Philosophy of Nature._--This is a strong argument, _a priori_,
but is subject to re-interpretation, in the light of new facts, to which
it must conform. Facts might be adduced which proved this particular
view of nature wrong. It is, in short, only a working hypothesis,
subject to revision, as new facts are adduced, tending to alter it.

6. _Psychology._--Our ignorance of the possible relation of brain and
mind is no excuse for our dogmatically asserting that no such connection
is possible. It may be a fact, though unintelligible to us. Mental
states may influence, partially at least, successive brain-states. We
cannot say. If one man asserts that they _cannot_, another may assert
that they _do_. Hence every one is at liberty to believe what he
pleases! Nothing is proved.

If, now, we glance at the preceding arguments, we find that they may be
summarized somewhat as follows:

Arguments 2, 3, 5, and 6 are practically valueless, one way or the
other. Both sides might claim a victory; none of these arguments would
settle the question.

Argument 4 is certainly valid, to a certain extent, and can only be
surmounted by assuming that a non-physical energy can affect physical
energy. But I do not think that any physicist would be inclined to admit
this. So that this argument cannot be used in support of the doctrine of
Free Will.

There remains the first argument, drawn from the law of the Conservation
of Energy. This is certainly the strongest of all (to my mind), and is,
as it stands, valid. Though idealism may maintain that all physical
energy may be, in its ultimate analysis, only psychical energy, I do not
for a moment believe that any physicist really believes this, or that
any man accepts it as a common-sense doctrine--one which can be acted
upon in daily life. It is mere philosophical sophistry and
hairsplitting, and we must believe, as a matter of fact, that physical
energy _is_ really physical, and not psychical, in its nature.

As to the first portion of this argument, although the law of
Conservation of Energy has never been shown to be invalid, when applied
to the connection of brain and mind, still, every one probably believes
that it does actually obtain, and that a brain-state cannot result in
consequence of non-physical influences any more than any other physical
event could so result. It is tacitly admitted, therefore, that the law
of Conservation holds good here also, and that will cannot affect brain,