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 con