The Critique of Pure Reason | Page 6

When Galilei experimented with balls of a definite weight on the
inclined plane, when Torricelli caused the air to sustain a weight which
he had calculated beforehand to be equal to that of a definite column of
water, or when Stahl, at a later period, converted metals into lime, and
reconverted lime into metal, by the addition and subtraction of certain
elements; [Footnote: I do not here follow with exactness the history of
the experimental method, of which, indeed, the first steps are involved
in some obscurity.] a light broke upon all natural philosophers. They
learned that reason only perceives that which it produces after its own
design; that it must not be content to follow, as it were, in the
leading-strings of nature, but must proceed in advance with principles
of judgement according to unvarying laws, and compel nature to reply
its questions. For accidental observations, made according to no
preconceived plan, cannot be united under a necessary law. But it is
this that reason seeks for and requires. It is only the principles of reason
which can give to concordant phenomena the validity of laws, and it is
only when experiment is directed by these rational principles that it can
have any real utility. Reason must approach nature with the view,
indeed, of receiving information from it, not, however, in the character
of a pupil, who listens to all that his master chooses to tell him, but in
that of a judge, who compels the witnesses to reply to those questions
which he himself thinks fit to propose. To this single idea must the

revolution be ascribed, by which, after groping in the dark for so many
centuries, natural science was at length conducted into the path of
certain progress.
We come now to metaphysics, a purely speculative science, which
occupies a completely isolated position and is entirely independent of
the teachings of experience. It deals with mere conceptions--not, like
mathematics, with conceptions applied to intuition--and in it, reason is
the pupil of itself alone. It is the oldest of the sciences, and would still
survive, even if all the rest were swallowed up in the abyss of an
all-destroying barbarism. But it has not yet had the good fortune to
attain to the sure scientific method. This will be apparent; if we apply
the tests which we proposed at the outset. We find that reason
perpetually comes to a stand, when it attempts to gain a priori the
perception even of those laws which the most common experience
confirms. We find it compelled to retrace its steps in innumerable
instances, and to abandon the path on which it had entered, because this
does not lead to the desired result. We find, too, that those who are
engaged in metaphysical pursuits are far from being able to agree
among themselves, but that, on the contrary, this science appears to
furnish an arena specially adapted for the display of skill or the exercise
of strength in mock-contests-- a field in which no combatant ever yet
succeeded in gaining an inch of ground, in which, at least, no victory
was ever yet crowned with permanent possession.
This leads us to inquire why it is that, in metaphysics, the sure path of
science has not hitherto been found. Shall we suppose that it is
impossible to discover it? Why then should nature have visited our
reason with restless aspirations after it, as if it were one of our
weightiest concerns? Nay, more, how little cause should we have to
place confidence in our reason, if it abandons us in a matter about
which, most of all, we desire to know the truth--and not only so, but
even allures us to the pursuit of vain phantoms, only to betray us in the
end? Or, if the path has only hitherto been missed, what indications do
we possess to guide us in a renewed investigation, and to enable us to
hope for greater success than has fallen to the lot of our predecessors?

It appears to me that the examples of mathematics and natural
philosophy, which, as we have seen, were brought into their present
condition by a sudden revolution, are sufficiently remarkable to fix our
attention on the essential circumstances of the change which has proved
so advantageous to them, and to induce us to make the experiment of
imitating them, so far as the analogy which, as rational sciences, they
bear to metaphysics may permit. It has hitherto been assumed that our
cognition must conform to the objects; but all attempts to ascertain
anything about these objects a priori, by means of conceptions, and
thus to extend the range of our knowledge, have been rendered abortive
by this assumption. Let us then make the experiment whether we may
not be more successful in