This ground for the identification of the categories with the principles of synthesis involved in knowledge may be ignored, as on the face of it unsuccessful. For the argument is that since the activity by which the synthesis is affected is that of judgement, the conceptions shown by the _Metaphysical Deduction_ to be involved in judgement must constitute the principles of synthesis. But it is essential to this argument that the present account of judgement and that which forms the basis of the _Metaphysical Deduction_ should be the same; and this is plainly not the case.[91] Judgement is now represented as an act by which we relate the manifold of sense in certain necessary ways as parts of the physical world,[92] whereas in the _Metaphysical_ _Deduction_ it was treated as an act by which we relate conceptions; and Kant now actually says that this latter account is faulty. Hence even if the metaphysical deduction had successfully derived the categories from the account of judgement which it presupposed, the present argument would not justify the identification of the categories so deduced with the principles of synthesis. The fact is that Kant's vindication of the categories is in substance independent of the _Metaphysical Deduction_. Kant's real thought, as opposed to his formal presentation of it, is simply that when we come to consider what are the principles of synthesis involved in the reference of the manifold to an object, we find that they are the categories.[93] The success, then, of this step in Kant's vindication of the categories is independent of that of the metaphysical deduction, and depends solely upon the question whether the principles of synthesis involved in knowledge are in fact the categories. [91] Cf. Caird, i. 348-9 note. [92] We may notice in passing that this passage renders explicit the extreme difficulty of Kant's view that 'the objective unity of apperception' is the unity of the parts of nature or of the physical world. How can the 'very same representations' stand at once in the subjective relation of association and in the objective relation which consists in their being related as parts of nature? There is plainly involved a transition from representation, in the sense of the apprehension of something, to representation, in the sense of something apprehended. It is objects apprehended which are objectively related; it is our apprehensions of objects which are associated, cf. pp. 233 and 281-2. Current psychology seems to share Kant's mistake in its doctrine of association of ideas, by treating the elements associated, which are really apprehensions of objects, as if they were objects apprehended. [93] Cf. A. 112, Mah. 204; B. 162, M. 99.