Such is the form in which Kant’s pre-Critical doctrine of the transcendental object survives in the _Critique_.[801] It contains no trace of the teaching of the objective deduction of the first and second edition or of the teaching of the refutation of idealism in the second edition. It closely resembles Mill’s doctrine of the permanent possibilities of sensation, and is almost equally subjectivist in character. As already noted,[802] it also lies open to the further objection that it involves an illegitimate application of the categories to things in themselves. As Kant started from the naïve and natural assumption that reference of representations to objects must be their reference to things in themselves, he also took over the current Cartesian view that it is by an inference in terms of the category of causality that we advance from a representation to its cause. The thing in itself is regarded as the sole true substance and as the real cause of everything which happens in the natural world. Appearances, being representations merely, are wholly transitory and completely inefficacious. _Not only, therefore, are the categories regarded as valid of things in themselves, they are also declared to have no possible application to phenomena._ Sense appearances do not, on this view, constitute the mechanical world of the natural sciences; they have a purely subjective, more or less epi-phenomenal, existence in the mind of each separate observer. It was very gradually, in the process of developing his own Critical teaching, that Kant came to realise the very different position to which he was thereby committed. The categories, including that of causality, are pre-empted for the _empirical_ object which is now regarded as immediately apprehended; and the function of mediating the reference of phenomena to things in themselves now falls to the Ideas of Reason. The distinction between appearance and reality is no longer that between representations and their noumenal causes, but between the limited and relative character of the entire world in space and time and the unconditioned demanded by Reason. But these are questions whose discussion must meantime be deferred.[803]