  (3) The third objection, though repeated in a variety of ways, consists essentially in a criticism of Kant’s analysis of the function of the understanding in experience. Even granted all the elements of Kant’s transcendental psychology, notably, that sensations are per se amorphous mental impressions, that space and time can be at once intuitions and objects of intuition, that the categories are a priori concepts of the understanding — assumptions these, all of which Jacobi in fact rejects, and against which he strenuously argues in the body of the essay — even granted these, there still is an internal defect in Kant’s system. The problem is that the two terms to be synthesized in any presumed a priori judgement of experience, namely, thought and sensations, are on their own too indeterminate to provide any clue as to how the object that should result from the synthesis would look like. So far as sensibility is concerned, such indetermination applies whether we take it according to its material content or its a priori forms of intuition, for ‘space’ and ‘time’, as defined by Kant, lack per se definite limits (Jacobi, 1812–25: vol. 2, 77–79, 122ff, 134–35, 136–39). It follows that the determination, in actual experience, must be provided by the intervention of the imagination, and whether we take the latter in a psychological or transcendental sense, its contribution will necessarily entail an element of arbitrariness, and it will thus render any synthesis thereby attained vulnerable to sceptical doubt. Kant, in other words, fails to deliver on his promise of a knowledge, limited indeed to experience, but necessary within such limits (Jacobi, 1812–25: vol. 2, 95, 97, 115ff, 118ff, 135, 150, 154ff).