M ETAPHYSIC S. 
222 
one can prove, fince the object lies beyond the bounds of 
human underftanding. The eflential limitation of tliefe 
principles therefore is, that all objeXs rank necefl'arily 
under them, only as objefls of experience. 
Hence arifes a fpecific and peculiar proof of thefe prin- 
eioles ; namely, that they do not refer ftriXly to the phe¬ 
nomena, but to the poff bilily of experience itfelf; of which 
the phenomena coifftitute only the matter, and not the 
form ; that is to fay, that they are objectively and imi- 
verfally valid fynthetical pojitions, which diftinguifii judg¬ 
ments of experience from mere, judgments of apprehenlion. 
We are now enabled to remove radically Hume’s doubt. 
He juftly maintained, that we cannot at all perceive or 
difeover by reafon the pofiibility of CauJaHty ; i. e. of the 
relation of the exigence of one thing to the exiltence of 
fomething el/e, as its neceffary confequence. I mull add 
alfo, that we are ju/tas little able to conceive the neceflity 
of Subfftence, or that a liibjeX forms the foundation of 
the exiltence of things, which fubjeX itfelf cannot be a 
predicate of any other ; nay, even that w r e cannot form to 
ourfelves a conception of the pofiibility of fuch a fubjeX, 
(although we are able to exhibit in experience inftances 
of its ufe.) In like manner I afiert, that this very incon¬ 
ceivability involves al/o the Concurrence of things, iince 
it cannot be conceived how we can infer from the Itate of 
one-thing a confequence with refpeX to the Hate of other 
things, and this reciprocally; or how fubftances, each of 
which has its own feparate exiftence, can depend upon 
one another, and that necefl'arily. Neverthelefs, I am far 
from confidering thefe conceptions as borrowed from ex¬ 
perience, and their necefiity as fi£Ht.ious, and a mere illu- 
fion, with which long habit deceives us ; on the contrary, 
I have fufficiently Ihown that thefe conceptions and the 
principles derived from them Hand firm a priori, i. e. in¬ 
dependent of all experience, and are therefore undoubt¬ 
edly true, but indeed only for the ufe of experience. 
Though I have not the leaft conception of fuch a con¬ 
nexion of the things in themfelves, how they exift as 
Sulftance, or operate as Caufe, or Hand in Concurrence as 
parts of a whole ; and though I can /till le/s think of 
luch properties in the phenomena as phenomena, fince 
thefe conceptions contain nothing which belongs to the 
phenomena but what the underftanding, according to its. 
very nature, is compelled to place there ; yet I do really find 
fuch a connexion of reprefentations in the underftanding 
itfelf, and in judgment in general; that is to fay, I find 
the reprefentations in one kind of judgment Handing in 
the relation of fubjedl to predicate, in another as ground to 
confequence, and in a third as parts conftituting a whole. 
We know alfo, a priori, that, without confidering the re- 
prefentation of an objeX as determined in one or other 
of thefe ways, we could not have any knowledge of it. 
If, on the other hand, I am to meddle with the objcCl in 
itfelf, there is no one poflible mark by which I can know 
it to be determined according to either of the above re¬ 
lations ; that is to. fay, that it ranks under either the 
conception of Sulftance, of Canfe, or of Concurrence; for 
of the pofiibility of fuch a connexion of ex fences inde¬ 
pendent of the mind, I ha ve no conception. But the quef- 
tion is not how the things in themfelves are determined, 
but how our experience is determined by the above forms 
of Judgment in general, i. e. on what ground objeXs of 
experience can be fubfumpted under thefe conceptions 
of the underftanding. And hence it is clear, that I can 
perfeXly conceive, not only the pofiibility, but alfo the 
necefiity, of fubfumpting all phenomena under thefe con¬ 
ceptions ; i. e. the neceflity of uiing them as principles of 
the pofiibility of experience. 
. In confidering Hume’s problematical conception of 
Cause, his Crux Metaphyficorum, in the firft place, Logic 
furniflies us a priori with the form of a Conditional judg¬ 
ment in general; namely, the rule to ufe one given Know¬ 
ledge as a ground, and another as a confequence. In the 
apprehenfon, however, we may meet with a rule of rela¬ 
tion, according to which one phenomenon is conftantly 
followed by another, though not converfely; in this cafe 
we employ an hypothetical Judgment, and fay, for in- 
ftance, If a body be expofed for a certain time to the fun it. 
becomes war n: here, however, is no politive necefiti / of 
the connexion; consequently no conception of Canfe. 
In order to render the above polition, which is merely a 
JubjeCtive connexion of apprehenlions, a polition of expe¬ 
rience, it muff be conceived as neceflary and uiiiverfally 
valid. To exprefs this, we mult /'ay, The Sun is the canfe 
of heat. This empirical rule is now confidered as a law, 
and not only valid of the phenomena, but valid of them 
for the fake of the pofiibility of experience, which requires 
conftant and therefore neceflary laws. I perceive, there¬ 
fore, that the conception of caufe is a conception necef- 
farily belonging to the mere form of experience, and to 
its pofiibility as a fynthetical union of apprehen/ions in a 
confcioufnefs ; but the pofiibility of a thing in itfelf as a. 
Caufe, I cannot conceive at ail; and indeed' for this 
reafon, becaufe the conception of caule denotes no con¬ 
dition inherent in the things themfelves, but merely in 
experience, which is indeed only poflibie, and can only 
furnilh objeXively-valid knowledge of the phenomena, 
and of their fucceflion, in io far as the preceding can be 
conneXed with the fucceeding, according to the rule of 
hypothetical judgment. 
The pure conceptions of underfunding (Categories),there¬ 
fore, have no figniiication at all when they are l'eparated 
from objeXs of experience, and are applied to the things 
.in themfelves, (noumena.) They ferve, as it were, only 
to fpell the phenomena, in order to enable us to read 
them as experience. The principles which arife from 
their reference to the phenomena, or to the fenfible world, 
ferve the underftanding only for the purpofe of experi¬ 
ence, beyond which they are mere arbitrary connexions, 
without objeXive reality. For that-the/e principles apply 
to things in themfelves, we can neither know d priori, not 
prove by any example; nor can we even render it intel¬ 
ligible to ourfelves. 
This complete folution of Hume’s problem, though 
turning out contrary to the fuppofition of the author, 
reftores to the pure conceptions of underftanding their 
origin a priori, and to the univerfal laws of nature their 
validity, as laws of the underftanding; yet with this con¬ 
dition, that it limits their ufe to experience only, fince 
their very pofiibility is grounded merely in the reference 
of the underftanding to experience; not, however, that 
they are derived from experience, but experience from 
them ; which very oppofite mode of accounting for them 
never entered Hume’s mind. 
The reiult of all thefe investigations is then as follows : 
AU fynthetical principles d priori are nothing but principles 
of poffible experience, and can never be referred to the things 
in themfelves, but only to the phenomena as objeXs of 
experience. Hence alfo both pure Mathematics and pure 
Natural Philofophy can be applied only to the pheno¬ 
mena, and can reprefent nothing more than what expe¬ 
rience renders poftible. 
And thus we have at length fomething determined on 
which we may rely, notwithftanding all the metaphyfical 
attempts which have hitherto boldly and blindly tref- 
paffed every-where and upon every ti.ing. It never en¬ 
tered the minds of the dogmatical philoiophers that the 
end of their exertions was fo near at hand, nor indeed 
even into the minds of thofe who boaft of their common 
fenfe, and who proceed indeed upon juft and natural 
conceptions, and principles derived from pure reafon, 
but which are intended foleiy for the ufe of experience; 
whereas they know no determined boundary to their ufe, 
nor indeed could they know any, fince they had never 
dreamt of, nor were able to conceive, the nature or even 
the pofiibility of a pure underftanding. 
The Naturalift in pure reafon, by which I mean one 
who has the lelf-confidence to decide in matters of Meta- 
phyiics without the help of lcience, may indeed pretend 
to have, long fmee, not only imagined by the prophetic 
fpirit 
