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its boundary line。
The celebrated David Hume was one of those geographers of human
reason who believe that they have given a sufficient answer to all
such questions by declaring them to lie beyond the horizon of our
knowledge… a horizon which； however； Hume was unable to determine。 His
attention especially was directed to the principle of causality； and
he remarked with perfect justice that the truth of this principle； and
even the objective validity of the conception of a cause； was not
commonly based upon clear insight； that is； upon a priori cognition。
Hence he concluded that this law does not derive its authority from
its universality and necessity； but merely from its general
applicability in the course of experience； and a kind of subjective
necessity thence arising； which he termed habit。 From the inability of
reason to establish this principle as a necessary law for the
acquisition of all experience； he inferred the nullity of all the
attempts of reason to pass the region of the empirical。
This procedure of subjecting the facta of reason to examination；
and； if necessary； to disapproval； may be termed the censura of
reason。 This censura must inevitably lead us to doubts regarding all
transcendent employment of principles。 But this is only the second
step in our inquiry。 The first step in regard to the subjects of
pure reason； and which marks the infancy of that faculty； is that of
dogmatism。 The second； which we have just mentioned； is that of
scepticism； and it gives evidence that our judgement has been improved
by experience。 But a third step is necessary… indicative of the
maturity and manhood of the judgement； which now lays a firm
foundation upon universal and necessary principles。 This is the period
of criticism； in which we do not examine the facta of reason； but
reason itself； in the whole extent of its powers； and in regard to its
capability of a priori cognition； and thus we determine not merely the
empirical and ever…shifting bounds of our knowledge； but its necessary
and eternal limits。 We demonstrate from indubitable principles； not
merely our ignorance in respect to this or that subject； but in regard
to all possible questions of a certain class。 Thus scepticism is a
resting place for reason； in which it may reflect on its dogmatical
wanderings and gain some knowledge of the region in which it happens
to be； that it may pursue its way with greater certainty； but it
cannot be its permanent dwelling…place。 It must take up its abode only
in the region of complete certitude； whether this relates to the
cognition of objects themselves； or to the limits which bound all
our cognition。
Reason is not to be considered as an indefinitely extended plane； of
the bounds of which we have only a general knowledge； it ought
rather to be compared to a sphere； the radius of which may be found
from the curvature of its surface… that is； the nature of a priori
synthetical propositions… and； consequently； its circumference and
extent。 Beyond the sphere of experience there are no objects which
it can cognize； nay； even questions regarding such supposititious
objects relate only to the subjective principles of a complete
determination of the relations which exist between the
understanding…conceptions which lie within this sphere。
We are actually in possession of a priori synthetical cognitions； as
is proved by the existence of the principles of the understanding；
which anticipate experience。 If any one cannot comprehend the
possibility of these principles； he may have some reason to doubt
whether they are really a priori； but he cannot on this account
declare them to be impossible； and affirm the nullity of the steps
which reason may have taken under their guidance。 He can only say：
If we perceived their origin and their authenticity； we should be able
to determine the extent and limits of reason； but； till we can do
this； all propositions regarding the latter are mere random
assertions。 In this view； the doubt respecting all dogmatical
philosophy； which proceeds without the guidance of criticism； is
well grounded； but we cannot therefore deny to reason the ability to
construct a sound philosophy； when the way has been prepared by a
thorough critical investigation。 All the conceptions produced； and all
the questions raised； by pure reason； do not lie in the sphere of
experience； but in that of reason itself； and hence they must be
solved； and shown to be either valid or inadmissible； by that faculty。
We have no right to decline the solution of such problems； on the
ground that the solution can be discovered only from the nature of
things； and under pretence of the limitation of human faculties； for
reason is the sole creator of all these ideas； and is therefore
bound either to establish their validity or to expose their illusory
nature。
The polemic of scepticism is properly directed against the
dogmatist； who erects a system of philosophy without having examined
the fundamental objective principles on which it is based； for the
purpose of evidencing the futility of his designs； and thus bringing
him to a knowledge of his own powers。 But； in itself； scepticism
does not give us any certain information in regard to the bounds of
our knowledge。 All unsuccessful dogmatical attempts of reason are
facia； which it is always useful to submit to the censure of the
sceptic。 But this cannot help us to any decision regarding the
expectations which reason cherishes of better success in future
endeavours； the investigations of scepticism cannot； therefore； settle
the dispute regarding the rights and powers of human reason。
Hume is perhaps the ablest and most ingenious of all sceptical
philosophers； and his writings have； undoubtedly； exerted the most
powerful influence in awakening reason to a thorough investigation
into its own powers。 It will； therefore； well repay our labours to
consider for a little the course of reasoning which he followed and
the errors into which he strayed； although setting out on the path
of truth and certitude。
Hume was probably aware； although he never clearly developed the
notion； that we proceed in judgements of a certain class beyond our
conception if the object。 I have termed this kind of judgement
synthetical。 As regard the manner in which I pass beyond my conception
by the aid of experience； no doubts can be entertained。 Experience
is itself a synthesis of perceptions； and it employs perceptions to
increment the conception； which I obtain by means of another
perception。 But we feel persuaded that we are able to proceed beyond a
conception； and to extend our cognition a priori。 We attempt this in
two ways… either； through the pure understanding； in relation to
that which may become an object of experience； or； through pure
reason； in relation to such properties of things； or of the
existence of things； as can never be presented in any experience。 This
sceptical philosopher did not distinguish these two kinds of
judgements； as he ought to have done； but regarded this augmentation
of conceptions； and； if we may so express ourselves； the spontaneous
generation of understanding and reason； independently of the
impregnation of experience； as altogether impossible。 The so…called
a priori principles of these faculties he consequently held to be
invalid and imaginary； and regarded them as nothing but subjective
habits of thought originating in experience； and therefore purely
empirical and contingent rules； to which we attribute a spurious
necessity and universality。 In support of this strange assertion； he
referred us to the generally acknowledged principle of the relation
between cause and effect。 No faculty of the mind can conduct us from
the conception of a thing to the existence of something else； and
hence he believed he could infer that； without experience； we
possess no source from which we can augment a conception； and no
ground sufficient to justify us in framing a judgement that is to
extend our cognition a priori。 That the light of the sun； which shines
upon a piece of wax； at the same time melts it； while it hardens clay；
no power of the understanding could infer from the conceptions which
we previously possessed of these substances； much less is there any
a priori law that could conduct us to such a conclusion； which
experience alone can certify。 On the other hand； we have seen in our
discussion of transcendental logic； that； although we can never
proceed immediately beyond the content of the conception which is
given us； we can always cognize completely a priori… in relation；
however； to a third term； namely； possible experience… the law of
its connection with other things。 For example； if I observe that a
piece of wax melts； I can cognize a priori that there must have been
something （the sun's heat） preceding； which this law； although；
without the aid of experience； I could not cognize a priori and