Since the Essays of Locke and Leibniz, or rather since the origin of metaphysics so
far as we know its history, nothing has ever happened which could have been more decisive
to its fate than the attack made upon it by David Hume.
He threw no light on this kind of knowledge; but he certainly struck a spark from which
light might have been obtained, had it caught some inflammable substance and had its smouldering
fire been carefully nursed and developed.
Hume started mainly from a single but important concept in metaphysics, namely, that of the
connection of cause and effect (including its derivative concepts of force and action, etc.).
He challenged reason, which pretends to have given birth to this concept of herself, to
answer him by what right she thinks anything could be so constituted that if that thing
be posited, something else also must necessarily be posited; for this is the meaning of the
concept of cause.
He demonstrated irrefutably that it was entirely impossible for reason to think a priori and
by means of concepts such a combination as involves necessity.
We cannot at all see why, in consequence of the existence of one thing, another must necessarily
exist, or how the concept of such a combination can arise a priori.
Hence he inferred that reason was altogether deluded with reference to this concept, which
she erroneously considered as one of her children, whereas in reality it was nothing but a bastard
of imagination, impregnated by experience, which subsumed certain representations under
the law of association, and mistook a subjective necessity (custom) for an objective necessity
arising from insight.
Hence he inferred that reason had no power to think such connections, even in general,
because her concepts would then be purely fictitious and all her pretended a priori
cognitions nothing but common experiences marked with a false stamp.
This is as much as to say that there is not, and cannot be, any such thing as metaphysics at all.
Footnote. Nevertheless Hume called such destructive philosophy metaphysics and attached to it
great value.
"Metaphysics and morals," he says, "are the most important branches of science; mathematics
and natural philosophy are not half so important."
But the acute man merely regarded the negative use arising from the moderation of extravagant
claims of speculative reason, and the complete settlement of the many endless and troublesome
controversies that mislead mankind.
He overlooked the positive injury which results if reason be deprived of its most important
prospects, which can alone supply to the will the highest aim for all its endeavors.
However hasty and mistaken Hume's conclusion may appear, it was at least founded upon investigation,
and this investigation deserved the concentrated attention of the brighter spirits of his day
as well as determined efforts on their part to discover, if possible, a happier solution
of the problem in the sense proposed by him, all of which would have speedily resulted
in a complete reform of the science.
I openly confess that my remembering David Hume was the very thing which many years ago
first interrupted my dogmatic slumber and gave my investigations in the field of speculative
philosophy a quite new direction.
I was far from following him in the conclusions to which he arrived by considering, not the
whole of his problem, but a part, which by itself can give us no information.
If we start from a well-founded, but undeveloped, thought which another has bequeathed to us,
we may well hope by continued reflection to advance further than the acute man to whom
we owe the first spark of light.
So I tried first whether Hume's objection could not be put into a general form, and
soon found that the concept of the connection of cause and effect was by no means the only
concept by which the understanding thinks the connection of things a priori, but rather
that metaphysics consists altogether of such concepts.
I sought to ascertain their number; and when I had satisfactorily succeeded in this by
starting from a single principle, I proceeded to the deduction of these concepts, which
I was now certain were not derived from experience, as Hume had tried,
but sprang from the pure understanding.
This deduction (which seemed impossible to my acute predecessor and had never even occurred
to any one else, though no one had hesitated to use the concepts without investigating
the basis of their objective validity) was the most difficult task ever undertaken in
the service of metaphysics; and the worst was that metaphysics, such as it then existed,
could not assist me in the least because this deduction alone can render metaphysics possible.
But as soon as I had succeeded in solving Hume's problem, not merely in a particular
case, but with respect to the whole faculty of pure reason, I could proceed safely, though
slowly, to determine the whole sphere of pure reason completely and from universal principles,
in its boundaries as well as in its contents.
This was required for metaphysics in order to construct its system according to a sure plan.