How Are Synthetic a priori Judgments Possible?
Treatment of detailed points will be simplified if we now consider in systematic fashion the many difficulties that present themselves in connection with Kant’s mode of formulating his central problem: How are synthetic a priori judgments possible? This formula is less definite and precise than would at first sight appear. The central phrase ‘synthetic a priori’ is sufficiently exact (the meaning to be attached to the a priori has already been considered[175]), but ambiguities of the most various kinds lurk in the seemingly innocent and simple terms with which the formula begins and ends:
A. ‘How’ has two very different meanings:
(a) How possible = in what manner possible = wie.
(b) How possible = in how far possible, i.e. whether possible = ob.
In connection with these two meanings of the term ‘how,’ we shall have to consider the distinction between the synthetic method employed in the Critique and the analytic method employed in the Prolegomena.
B. ‘Possible’ has a still wider range of application. Vaihinger[176] distinguishes within it no less than three pairs of alternative meanings:
(a) Psychological and logical possibility.
(b) Possibility of explanation and possibility of existence.
(c) Real and ideal possibility.