THE POSTULATES OF EMPIRICAL THOUGHT
The postulates of empirical thought, which correspond to the
categories of modality, are stated as follows:
"1. That which agrees with the formal conditions of experience
(according to perception and conceptions) is _possible_.
2. That which is connected with the material conditions of experience
(sensation) is _actual_.
3. That of which the connexion with the actual is determined according
to universal conditions of experience is _necessary_ (exists
necessarily)."[1]
[1] B. 265-6, M. 161.
These principles, described as only 'explanations of the conceptions
of possibility, actuality, and necessity as employed in experience',
are really treated as principles by which we decide what is possible,
what is actual, and what is necessary. The three conceptions involved
do not, according to Kant, enlarge our knowledge of the nature of
objects, but only 'express their relation to the faculty of
knowledge'[2]; i. e. they only concern our ability to apprehend an
object whose nature is already determined for us otherwise as at least
possible, or as real, or as even necessary. Moreover, it is because
these principles do not enlarge our knowledge of the nature of objects
that they are called postulates; for a postulate in geometry, from
which science the term is borrowed (e. g. that it is possible with a
given line to describe a circle from a given point), does not augment
the conception of the figure to which it relates, but only asserts the
possibility of the conception itself.[3] The discussion of these
principles is described, contrary to the terminology adopted in the
case of the preceding principles, as 'explanation' and not as 'proof'.
The discussion, however, certainly includes a proof of them, for it is
Kant's main object to _prove_ that these principles constitute the
general character of what can be asserted to be possible, actual, or
necessary respectively. Again, as before, the basis of proof lies in a
theory of knowledge, and in particular in Kant's theory of knowledge;
for it consists in the principle that everything knowable must conform
to the conditions involved in its being an object of possible
experience.
[2] B. 266, M. 161. Cf. B. 286-7, M. 173-4.
[3] B. 286-7, M. 173-4.
To understand these principles and the proof of them, we must notice
certain preliminary considerations. In the _first_ place, the very
problem of distinguishing the possible, the actual, and the necessary
presupposes the existence of distinctions which may prove open to
question. It presupposes that something may be possible without being
actual, and again that something may be actual without being
necessary. In the _second_ place, Kant's mode of approaching the
problem assumes that we can begin with a conception of an object,
e. g. of a man with six toes, and then ask whether the object of it is
possible, whether, if possible, it is also actual, and whether, if
actual, it is also necessary. In other words, it assumes the
possibility of separating what is conceived from what is possible, and
therefore _a fortiori_ from what is actual,[4] and from what is
necessary. _Thirdly_, in this context, as in most others, Kant in
speaking of a conception is thinking, to use Locke's phraseology, not
of a 'simple' conception, such as that of equality or of redness, but
of a 'complex' conception, such as that of a centaur, or of a triangle
in the sense of a three-sided three-angled figure. It is the
apprehension of a 'complex' of elements.[5] _Fourthly_, what is said
to be possible, real, or necessary is not the conception but the
corresponding object. The question is not, for instance, whether the
conception of a triangle or of a centaur is possible, actual, or
necessary, but whether a triangle or a centaur is possible, actual, or
necessary. Kant sometimes speaks loosely of conceptions as
possible,[6] but the terms which he normally and, from the point of
view of his theory, rightly applies to conceptions are 'objectively
real' and 'fictitious'.[7] _Lastly_, Kant distinguishes 'objectively
real' and 'fictitious' conceptions in two ways. He speaks of
establishing the objective reality of a conception as consisting in
establishing the possibility of a corresponding object,[8] implying
therefore that a fictitious conception is a conception of which the
corresponding object is not known to be possible. Again, he describes
as fictitious new conceptions of substances, powers, and interactions,
which we might form from the material offered to us by perception
without borrowing from experience itself the example of their
connexions, e. g. the conception of a power of the mind to perceive
the future; and he says that the possibility of these conceptions
(i. e. the possibility of corresponding objects) cannot, like that of
the categories, be acquired _a priori_ through their being conditions
on which all experience depends, but must be discovered empirically or
not at all. Of such conceptions he says that, without being based upon
experience and its known laws, they are arbitrary syntheses which,
although they contain no contradiction, have no claim to objective
reality, and therefore to the possibility of corresponding objects.[9]
He implies, therefore, that the object of a conception can be said to
be possible only when the conception is the apprehension of a complex
of elements together with the apprehension--which, if not _a priori_,
must be based upon experience--that they are connected. Hence a
conception may be regarded as 'objectively real', or as 'fictitious'
according as it is the apprehension of a complex of elements
accompanied by the apprehension that they are connected, or the
apprehension of a complex of elements not so accompanied.
[4] The view that 'in the mere conception of a thing no sign
of its existence is to be found' (B. 272, M. 165) forms, of
course, the basis of Kant's criticism of the ontological
argument for the existence of God. Cf. _Dialectic_, Bk. II,
Ch. III, Sec. 4.
[5] Cf. 'a conception which includes in itself a synthesis'
(B. 267 med., M. 162 med.).
[6] E. g. B. 269 fin., M. 163 fin.; B. 270 med., M. 164 init.
The formulation which really expresses Kant's thought is to
be found B. 266 med., M. 161 fin.; B. 268 init., M. 162 fin.;
B. 268 med., M. 163 init.; and B. 270 med., M. 164 init.
[7] _Gedichtete._
[8] B. 268 init., M. 162 fin.
[9] B. 269-70, M. 163-4.
It is now possible to state Kant's problem more precisely. With regard
to a given complex conception he wishes to determine the way in which
we can answer the questions (1) 'Has the conception a possible object
to correspond to it', or, in other words, 'Is the conception
'objectively real' or 'fictitious'?' (2) 'Given that a corresponding
object is possible, is it also real?' (3) 'Given that it is real, is
it also necessary?'
The substance of Kant's answer to this problem may be stated thus:
'The most obvious guarantee of the objective reality of a conception,
i. e. of the possibility of a corresponding object, is the experience
of such an object. For instance, our experience of water guarantees
the objective reality of the conception of a liquid which expands as
it solidifies. This appeal to experience, however, takes us beyond the
possibility of the object to its reality, for the experience
vindicates the possibility of the object only through its reality.
Moreover, here the basis of our assertion of possibility is only
empirical, whereas our aim is to discover the conceptions of which the
objects can be determined _a priori_ to be possible. What then is the
answer to this, the real problem? To take the case of cause and
effect, we cannot reach any conclusion by the mere study of the
conception of cause and effect. For although the conception of a
necessary succession contains no contradiction, the necessary
succession of events is a mere arbitrary synthesis as far as our
thought of it is concerned; we have no direct insight into the
necessity. Therefore we cannot argue from this conception to the
possibility of a corresponding object, viz. a necessarily successive
series of events in nature. We can, however, say that that synthesis
is not arbitrary but necessary to which any object must conform, if it
is to be an object of experience. From this point of view we can say
that there must be a possible object corresponding to the conception
of cause and effect, because only as subjected to this synthesis are
there objects of experience at all. Hence, if we take this point of
view, we can say generally that all spatial and temporal conceptions,
as constituting the conditions of perceiving in experience, and all
the categories, as constituting the conditions of conceiving in
experience, must have possible objects. In other words, 'that which
agrees with the formal conditions of experience (according to
perception and conceptions) is _possible_'. Again, if we know that
the object of a conception is possible, how are we to determine
whether it is also actual? It is clear that, since we cannot advance
from the mere conception, objectively real though it may be, to the
reality of the corresponding object, we need perception. The case,
however, where the corresponding object is directly perceived may be
ignored, for it involves no inference or process of thought; the
appeal is to experience alone. Therefore the question to be considered
is, 'How do we determine the actuality of the object of a conception
comparatively _a priori_, i. e. without direct experience of it[10]?'
The answer must be that we do so by finding it to be 'connected
with an actual perception in accordance with the analogies of
experience'[11]. For instance, we must establish the actuality of an
object corresponding to the conception of a volcanic eruption by
showing it to be involved, in accordance with the analogies (and with
particular empirical laws), in the state of a place which we are now
perceiving. In other words, we can say that 'that which is connected
with the material conditions of existence (sensation) is _actual_'.
Finally, since we cannot learn the existence of any object of
experience wholly _a priori_, but only relatively to another existence
already given, the necessity of the existence of an object can never
be known from conceptions, but only from its connexion with what is
perceived; this necessity, however, is not the necessity of the
existence of a substance, but only the necessity of connexion of an
unobserved state of a substance with some observed state of a
substance. Therefore we can (and indeed must) say of an unobserved
object corresponding to a conception, not only that it is real, but
also that it is necessary, when we know it to be connected with a
perceived reality 'according to universal conditions of experience';
but the necessity can be attributed only to states of substances and
not to substances themselves.'
[10] Cf. B. 279, M. 169 and p. 4, note 1.
[11] B. 273, M. 165.
Throughout this account there runs one fatal mistake, that of
supposing that we can separate our knowledge of things as possible, as
actual, and as necessary. Even if this supposition be tenable in
certain cases,[12] it is not tenable in respect of the objects of a
complex conception, with which Kant is dealing. If we know the object
of a complex conception to be possible, we already know it to be
actual, and if we know it to be actual, we already know it to be
necessary. A complex conception in the proper sense is the
apprehension of a complex of elements together with the apprehension
of, or insight into, their connexion.[13] Thus, in the case of the
conception of a triangle we see that the possession of three sides
necessitates the possession of three angles. From such a conception
must be distinguished Kant's 'fictitious' conception, i. e. the
apprehension of a complex of elements without the apprehension of
connexion between them. Thus, in the case of the conception of a man
with six toes, there is no apprehension of connexion between the
possession of the characteristics indicated by the term 'man' and the
possession of six toes. In such a case, since we do not apprehend any
connexion between the elements, we do not really 'conceive' or 'think'
the object in question, e. g. a man with six toes. Now in the case of
a complex conception proper, it is impossible to think of a
corresponding individual as only possible. The question 'Is a
triangle, in the sense of a figure with three sides and three angles,
possible?' really means 'Is it possible for a three-sided figure to
have three angles?' To this question we can only answer that we see
that a three-sided figure can have three angles, because we see that
it must have, and therefore has, and can have, three angles; in other
words, that we see a triangle in the sense in question to be possible,
because we see it to be necessary, and, therefore, actual, and
possible. It cannot be argued that our insight is limited to the fact
that if there are three-sided figures they must be three-angled, and
that therefore we only know a triangle in the sense in question to be
possible. Our apprehension of the fact that the possession of three
sides necessitates the possession of three angles presupposes
knowledge of the existence of three-sided figures, for it is only in
an actual three-sided figure that we can apprehend the necessity. It
may, however, be objected that the question ought to mean simply 'Is a
three-sided figure possible?' and that, understood in this sense, it
cannot be answered in a similar way. Nevertheless, a similar answer is
the right answer. For the question 'Is a three-sided figure possible?'
really means 'Is it possible for three straight lines to form a
figure, i. e. to enclose a space?' and we can only answer it for
ourselves by seeing that a group of three straight lines or
directions, no two of which are parallel, must, as such, enclose a
space, this insight presupposing the apprehension of an actual group
of three straight lines. It may be said, therefore, that we can only
determine the possibility of the object of a complex conception in
the proper sense, through an act in which we apprehend its necessity
and its actuality at once. It is only where conceptions are
'fictitious', and so not properly conceptions, that appeal to
experience is necessary. The question 'Is an object corresponding to
the conception of a man with six toes possible?' presupposes the
reality of man and asks whether any man can have six toes. If we
understood the nature of man and could thereby apprehend either that
the possession of six toes was, or that it was not, involved in one of
the possible differentiations of man, we could decide the question of
possibility _a priori_, i. e. through our conceiving alone without an
appeal to experience; but we could do so only because we apprehended
either that a certain kind of man with six toes was necessary and
actual, or that such a man was impossible and not actual. If, however,
as is the case, we do not understand the nature of man, we can only
decide the question of possibility by an appeal to experience, i. e.
to the experience of a corresponding object, or of an object from
which the existence of such an object could be inferred. Here,
therefore--assuming the required experience to be forthcoming--we
can appeal to Kant's formula and say that we know that such a man,
i. e. an object corresponding to the conception, is actual, as
being connected with the material conditions of experience. But the
perception which constitutes the material conditions of experience
in the case in question is only of use because it carries us beyond
possibility to actuality, and appeal to it is only necessary because
the object is not really conceived or, in other words, because the
so-called conception is not really a conception.
[12] For instance, it might at least be _argued_ that we know
space to be actual without knowing it to be necessary.
[13] _Not_ 'together with the apprehension _that_ the
elements are connected'. Cf. p. 311.
Kant really treats his 'objectively real' conceptions as if they were
'fictitious', even though he speaks of them as complete. Consequently,
his conceptions not being conceptions proper, he is necessarily led to
hold that an appeal to experience is needed in order to establish the
reality of a corresponding object. Yet, this being so, he should have
asked himself whether, without an appeal to perception, we could even
say that a corresponding object was possible. That he did not ask this
question is partly due to the fact that he attributes the form and the
matter of knowledge to different sources, viz. to the mind and to
things in themselves. While the conceptions involved in the forms of
perception, space, and time, and also the categories are the
manifestations of the mind's own nature, sensations, which form the
matter of knowledge, are due to the action of things in themselves on
our sensibility, and of this activity we can say nothing. Hence, from
the point of view of our mind--and since we do not know things in
themselves, this is the only point of view we can take--the existence
of sensations, and therefore of objects, which must be given in
perception, is wholly contingent and only to be discovered through
experience. On the other hand, since the forms of perception and
conception necessarily determine in certain ways the nature of
objects, _if_ there prove to be any objects, the conceptions involved
may be thought to determine what objects are possible, even though the
very existence of the objects is uncertain. Nevertheless, on his own
principles, Kant should have allowed that, apart from perception, we
could discover _a priori_ at least the reality, even if not the
necessity, of the objects of these conceptions. For his general view
is that the forms of perception and the categories are only actualized
on the occasion of the stimulus afforded by the action of things in
themselves on the sensibility. Hence the fact that the categories and
forms of perception are actualized--a fact implied in the very
existence of the _Critique_--involves the existence of objects
corresponding to the categories and to the conceptions involved in the
forms of perception. On Kant's own principles, therefore, we could say
_a priori_ that there must be objects corresponding to these
conceptions, even though their nature in detail could only be filled
in by experience.[14]
[14] Cf. Caird, i. 604-5.
NOTE ON THE REFUTATION OF IDEALISM
This well-known passage[1] practically replaces a long section,[2]
contained only in the first edition, on the fourth paralogism of
pure reason. Its aim is to vindicate against 'idealism' the reality
of objects in space, and it is for this reason inserted after the
discussion of the second postulate. The interest which it has excited
is due to Kant's use of language which at least seems to imply that
bodies in space are things in themselves, and therefore that here he
really abandons his main thesis.
[1] B. 274-9, M. 167-9. Cf. B. xxxix (note), M. xl (note).
[2] A. 367-80, Mah. 241-53.
Idealism is the general name which Kant gives to any view which
questions or denies the reality of the physical world; and, as has
been pointed out before,[3] he repeatedly tries to defend himself
against the charge of being an idealist in this general sense. This
passage is the expression of his final attempt. Kant begins by
distinguishing two forms which idealism can take according as it
regards the existence of objects in space as false and _impossible_,
or as doubtful and _indemonstrable_. His own view, which regards their
existence as certain and demonstrable, and which he elsewhere[4]
calls transcendental idealism, constitutes a third form. The first
form is the dogmatic idealism of Berkeley. This view, Kant says,
is unavoidable, if space be regarded as a property of things in
themselves, and the basis of it has been destroyed in the _Aesthetic_.
The second form is the problematic idealism of Descartes, according to
which we are immediately aware only of our own existence, and belief
in the existence of bodies in space can be only an inference, and an
uncertain inference, from the immediate apprehension of our own
existence. This view, according to Kant, is the outcome of a
philosophical attitude of mind, in that it demands that a belief
should be proved, and apparently--to judge from what Kant says of
Berkeley--it does not commit Descartes to the view that bodies in
space, if their reality can be vindicated, are things in themselves.
[3] Cf. p. 76.
[4] A. 369, Mah. 243; cf. B. 44, M. 27.
The assertion that the _Aesthetic_ has destroyed the basis of
Berkeley's view, taken together with the drift of the _Refutation_
as a whole, and especially of Remark I, renders it clear that the
_Refutation_ is directed against Descartes and not Berkeley. Kant
regards himself as having already refuted Berkeley's view, as he
here states it, viz. that the existence of objects in space is
_impossible_, on the ground that it arose from the mistake of
supposing that space, if real at all, must be a property of things in
themselves, whereas the _Aesthetic_ has as he thinks, shown that space
can be, and in point of fact is, a property of phenomena. He now wants
to prove--compatibly with their character as phenomena--that the
existence of bodies in space is not even, as Descartes contends,
_doubtful_. To prove this he seeks to show that Descartes is wrong in
supposing that we have no immediate experience of these objects. His
method is to argue that reflection shows that internal experience
presupposes external experience, i. e. that unless we were directly
aware of spatial objects, we could not be aware of the succession of
our own states, and consequently that it is an inversion to hold that
we must reach the knowledge of objects in space, if at all, by an
inference from the immediate apprehension of our own states.
An examination of the proof itself, however, forces us to allow that
Kant, without realizing what he is doing, really abandons the view
that objects in space are phenomena, and uses an argument the very
nature of which implies that these objects are things in themselves.
The proof runs thus:
_Theorem._ "The mere but empirically determined consciousness of my
own existence proves the existence of objects in space external to
me."
"_Proof._ I am conscious of my own existence as determined in
time. All time-determination presupposes something permanent in
perception.[5] This permanent, however, cannot be an intuition[6]
in me. For all grounds of determination of my own existence, which
can be found in me, are representations, and as such themselves need
a permanent different from them, in relation to which their change
and consequently my existence in the time in which they change can
be determined.[7] The perception of this permanent, therefore, is
possible only through a _thing_ external to me, and not through the
mere _representation_ of a thing external to me. Consequently, the
determination of my existence in time is possible only through the
existence of actual things, which I perceive external to me. Now
consciousness in time is necessarily connected with the consciousness
of the possibility of this time-determination; hence it is necessarily
connected also with the existence of things external to me, as the
condition of time-determination, i. e. the consciousness of my own
existence, is at the same time an immediate consciousness of the
existence of other things external to me."[8]
[5] _Wahrnehmung._
[6] _Anschauung._
[7] The text has been corrected in accordance with Kant's
note in the preface to the second edition, B. xxxix, M. xl.
[8] B. 275-6, M. 167.
The nature of the argument is clear. 'In order to be conscious, as
I am, of a determinate succession of my states, I must perceive
something permanent as that in relation to which alone I can perceive
my states as having a definite order.[9] But this permanent cannot be
a perception in me, for in that case it would only be a representation
of mine, which, as such, could only be apprehended in relation to
another permanent. Consequently, this permanent must be a thing
external to me and not a representation of a thing external to me.
Consequently, the consciousness of my own existence, which is
necessarily a consciousness of my successive states, involves the
immediate consciousness of things external to me.'
[9] Cf. Kant's proof of the first analogy.
Here there is no way of avoiding the conclusion that Kant is deceived
by the ambiguity of the phrase 'a thing external to me' into thinking
that he has given a proof of the existence of bodies in space which is
compatible with the view that they are only phenomena, although in
reality the proof presupposes that they are things in themselves. In
the 'proof', the phrase 'a thing external to me' must have a double
meaning. It must mean a thing external to my body, i. e. any body
which is not my body; in other words, it must be a loose expression
for a body in space. For, though the 'proof' makes us appeal to the
spatial character of things external to me, the _Refutation_ as a
whole, and especially Remark II, shows that it is of bodies in space
that he is thinking throughout. The phrase must also, and primarily,
mean a thing external to, in the sense of independent of, my mind,
i. e. a thing in itself. For the nerve of the argument consists in the
contention that the permanent the perception of which is required for
the consciousness of my successive states must be a _thing_ external
to me in opposition to the representation of a thing external to me,
and a thing external to me in opposition to a thing external to me can
only be a thing in itself. On the other hand, in Kant's conclusion,
'a thing external to me' can only mean a body in space, this being
supposed to be a phenomenon; for his aim is to establish the reality
of bodies in space compatibly with his general view that they are only
phenomena. The proof therefore requires that things external to me, in
order that they may render possible the consciousness of my successive
states, should have the very character which is withheld from them in
the conclusion, viz. that of existing independently of me; in other
words, if Kant establishes the existence of bodies in space at all,
he does so only at the cost of allowing that they are things in
themselves.[10]
[10] The ambiguity of the phrase 'external to me' is pointed
out in the suppressed account of the fourth paralogism,
where it is expressly declared that objects in space are
only representations. (A. 372-3, Mah. 247). Possibly the
introduction of an argument which turns on the view that they
are not representations may have had something to do with the
suppression.
Nevertheless, the _Refutation_ may be considered to suggest the proper
refutation of Descartes. It is possible to ignore Kant's demand for a
permanent as a condition of the apprehension of our successive states,
and to confine attention to his remark that he has shown that external
experience is really immediate, and that only by means of it is the
consciousness of our existence as determined in time possible.[11] If
we do so, we may consider the _Refutation_ as suggesting the view that
Descartes' position is precisely an inversion of the truth; in other
words, that our consciousness of the world, so far from being an
uncertain inference from the consciousness of our successive states,
is in reality a presupposition of the latter consciousness, in that
this latter consciousness only arises through reflection upon the
former, and that therefore Descartes' admission of the validity of
self-consciousness implicitly involves the admission _a fortiori_ of
the validity of our consciousness of the world.[12]
[11] B. 277, M. 167 fin.
[12] Cf. Caird, i. 632 and ff.
Oxford: Printed at the Clarendon Press by HORACE HART, M.A.