It can abstract altogether from the application of this notion to
objects with a view to theoretical knowledge （since this concept is
always found a priori in the understanding even independently of any
intuition）。 Reason； then； employs it only for a practical purpose； and
hence we can transfer the determining principle of the will into the
intelligible order of things； admitting； at the same time； that we
cannot understand how the notion of cause can determine the
knowledge of these things。 But reason must cognise causality with
respect to the actions of the will in the sensible world in a definite
manner； otherwise； practical reason could not really produce any
action。 But as to the notion which it forms of its own causality as
noumenon； it need not determine it theoretically with a view to the
cognition of its supersensible existence； so as to give it
significance in this way。 For it acquires significance apart from
this； though only for practical use； namely； through the moral law。
Theoretically viewed； it remains always a pure a priori concept of the
understanding； which can be applied to objects whether they have
been given sensibly or not； although in the latter case it has no
definite theoretical significance or application； but is only a
formal； though essential； conception of the understanding relating
to an object in general。 The significance which reason gives it
through the moral law is merely practical； inasmuch as the idea of the
idea of the law of causality （of the will） has self causality； or is
its determining principle。
II。 Of the Right that Pure Reason in its Practical use has to an
Extension which is not possible to it in its Speculative Use。
We have in the moral principle set forth a law of causality； the
determining principle of which is set above all the conditions of
the sensible world； we have it conceived how the will； as belonging to
the intelligible world； is determinable； and therefore we therefore we
have its subject （man） not merely conceived as belonging to a world of
pure understanding； and in this respect unknown （which the critique of
speculative reason enabled us to do）； but also defined as regards
his causality by means of a law which cannot be reduced to any
physical law of the sensible world； and therefore our knowledge is
extended beyond the limits of that world； a pretension which the
Critique of Pure Reason declared to be futile in all speculation。 Now；
how is the practical use of pure reason here to be reconciled with the
theoretical； as to the determination of the limits of its faculty？
David Hume； of whom we may say that he menced the assault on
the claims of pure reason； which made a thorough investigation of it
necessary； argued thus： The notion of cause is a notion that
involves the necessity of the connexion of the existence of
different things （and that； in so far as they are different）； so that；
given A； I know that something quite distinct there from； namely B；
must necessarily also exist。 Now necessity can be attributed to a
connection； only in so far as it is known a priori； for experience
would only enable us to know of such a connection that it exists；
not that it necessarily exists。 Now； it is impossible； says he； to
know a priori and as necessary the connection between one thing and
another （or between one attribute and another quite distinct） when
they have not been given in experience。 Therefore the notion of a
cause is fictitious and delusive and； to speak in the mildest way；
is an illusion； only excusable inasmuch as the custom （a subjective
necessity） of perceiving certain things； or their attributes as
often associated in existence along with or in succession to one
another； is insensibly taken for an objective necessity of supposing
such a connection in the objects themselves； and thus the notion of
a cause has been acquired surreptitiously and not legitimately； nay；
it can never be so acquired or authenticated； since it demands a
connection in itself vain； chimerical； and untenable in presence of
reason； and to which no object can ever correspond。 In this way was
empiricism first introduced as the sole source of principles； as far
as all knowledge of the existence of things is concerned
（mathematics therefore remaining excepted）； and with empiricism the
most thorough scepticism； even with regard to the whole science of
nature（ as philosophy）。 For on such principles we can never conclude
from given attributes of things as existing to a consequence （for this
would require the notion of cause； which involves the necessity of
such a connection）； we can only； guided by imagination； expect similar
cases… an expectation which is never certain； however of ten it has
been fulfilled。 Of no event could we say： a certain thing must have
preceded it； on which it necessarily followed； that is； it must have a
cause； and therefore； however frequent the cases we have known in
which there was such an antecedent； so that a rule could be derived
from them； yet we never could suppose it as always and necessarily
so happening； we should； therefore； be obliged to leave its share to
blind chance； with which all use of reason es to an end； and this
firmly establishes scepticism in reference to arguments ascending from
effects to causes and makes it impregnable。
Mathematics escaped well； so far； because Hume thought that its
propositions were analytical； that is； proceeded from one property
to another； by virtue of identity and； consequently； according to
the principle of contradiction。 This； however； is not the case； since；
on the contrary； they are synthetical； and although geometry； for
example； has not to do with the existence of things； but only with
their a priori properties in a possible intuition； yet it proceeds
just as in the case of the causal notion； from one property （A） to
another wholly distinct （B）； as necessarily connected with the former。
Nevertheless； mathematical science； so highly vaunted for its
apodeictic certainty； must at last fall under this empiricism for
the same reason for which Hume put custom in the place of objective
necessity in the notion of cause and； in spite of all its pride；
must consent to lower its bold pretension of claiming assent a
priori and depend for assent to the universality of its propositions
on the kindness of observers； who； when called as witnesses； would
surely not hesitate to admit that what the geometer propounds as a
theorem they have always perceived to be the fact； and；
consequently； although it be not necessarily true； yet they would
permit us to expect it to be true in the future。 In this manner Hume's
empiricism leads inevitably to scepticism； even with regard to
mathematics； and consequently in every scientific theoretical use of
reason （for this belongs either to philosophy or mathematics）。 Whether
with such a terrible overthrow of the chief branches of knowledge；
mon reason will escape better； and will not rather bee
irrecoverably involved in this destruction of all knowledge； so that
from the same principles a universal scepticism should follow
（affecting； indeed； only the learned）； this I will leave everyone to
judge for himself。
As regards my own labours in the critical examination of pure
reason； which were occasioned by Hume's sceptical teaching； but went
much further and embraced the whole field of pure theoretical reason
in its synthetic use and； consequently； the field of what is called
metaphysics in general； I proceeded in the following manner with
respect to the doubts raised by the Scottish philosopher touching
the notion of causality。 If Hume took the objects of experience for
things in themselves （as is almost always done）； he was quite right in
declaring the notion of cause to be a deception and false illusion；
for as to things in themselves； and their attributes as such； it is
impossible to see why because A is given； B； which is different；
must necessarily be also given； and therefore he could by no means
admit such an a priori knowledge of things in themselves。 Still less
could this acute writer allow an empirical origin of this concept；
since this is directly contradictory to t