Yesterday I wrote on my favorite philosopher from the Modern tradition, Immanuel Kant, and troubles for his theory – today I want to briefly touch on his critique of the man who began said tradition, Rene Descartes, in order to put Kant’s theory in context.
Kant sets his sights on Descartes’ rationalistic theory, but which Kant terms ‘idealistic’, which holds that the existence of external objects are doubtful and indemonstrable unless sufficient evidence can be given for them through reasoning. Kant calls this view ‘problematic idealism’. It is worth making clear that Kant opposes this position because it entails that the existence of objects are not known immediately through perception, but only through reasoned reflection. Problematic idealism, then, is the view that knowledge of external objects is reasoned from the indubitable existence of inner sense. Kant posits that problematic idealism is erroneous because external objects are necessary for the experience of inner sense, such that, inner sense cannot be used to prove the existence of external objects as the existence of inner sense presupposes the existence of external objects.
Problematic idealism is false, for Kant, because in order to have the sense of self necessary for reasoning to the existence of external objects, one must perceive their self as existing in time, and thus, know that they exist through time by the reference point of an external object. More specifically, Kant argues against problematic idealism by positing that the agent is aware that she is in time. In order to be aware that she is in time she must have a reference point, that is, something that endures through time, in order to know that her self endures through time as well. The reference point cannot be anything about her self, as this would be nothing more than her assuming that she exists in time. On this matter Kant notes that, “this permanent [reference point] cannot, however, be something in me, since it is only through this permanent that my existence in time can itself be determined” (Critique of Pure Reason, 245). In other words, in order to know that you are in time, the reference point cannot be yourself, as this would not be informative of whether you are in time. Thus, the reference point must be something other than the self, such that it must be an external object.
Yet if this is the case, then there must be real objects out in the world – not just representations of objects – which are known immediately in interacting with them, in order for one to have a concept of self. In Kant’s own words, “the consciousness of my existence is at the same time an immediate consciousness of the existence of other things outside me” (Critique of Pure Reason, 245). Therefore, problematic idealism, or Cartesian rationalism, is false because it denies that we immediately know that external objects exist in order to have inner sense.