This last phrase, ‘transcendental in a psychological sense,’ calls for a word of justification. The synthetic processes generative of experience are not, of course, transcendental in the strict sense. For they are not _a priori_ in the manner of the categories. None the less they are discoverable by the same transcendental method, namely, as being, like the categories, indispensably necessary to the possibility of experience. They differ from the categories in that they are not immanent in experience, constituent of it, and cannot therefore be known in their intrinsic nature. As they fall outside the field of consciousness, they can only be hypothetically postulated. None the less, formal categories and generative processes, definable elements and problematic postulates, alike agree in being conditions _sine qua non_ of experience. And further, in terms of Kant’s presupposed psychology, the latter are the source to which the former are due. There would thus seem to be sufficient justification for extending the term transcendental to cover both; and in so doing we are following the path which Kant himself willingly travelled. For such would seem to have been his unexpressed reasons for ascribing, as he does, the synthetic generative processes to what he himself names transcendental faculties. This disposes of Kant’s chief reason for refusing to recognise the subjective deduction as a genuine part of the Critical enquiry, namely, the contention upon which he lays such emphasis in the prefaces both of the first and of the second edition,[869] that in transcendental philosophy nothing hypothetical, nothing in any degree dependent upon general reasoning from contingent fact, can have any place. That contention proves untenable even within the domain of his purely logical analyses. The very essence of his transcendental method consists in the establishment of _a priori_ elements through proof of their connection with factual experience. Kant is here revealing how greatly his mind is still biased by the Leibnizian rationalism from which he is breaking away. His _a priori_ cannot establish itself save in virtue of hypothetical reasoning.[870] His transcendental method, rightly understood, does not differ in essential nature from the hypothetical method of the natural sciences; it does so only in the nature of its starting-point, and in the character of the analyses which that starting-point prescribes. And if hypothetical reasoning may be allowed in the establishment of the logical _a priori_, there is no sufficient reason why it may not also be employed for the determination of dynamical factors. The sole question is as to whether the hypotheses conform to the logical requirements and so raise themselves to a different level from mere opinion and conjecture.[871] As Kant himself says,[872] though his conclusions in the subjective deduction may seem to be hypothetical in the illegitimate sense, they are not really so.