Kant: Religion within the Boundaries of Mere Reason And Other Writings

However exalted the application of our concepts, and however far up from sensibility we may abstract them, still they will always be appended to image representations, whose proper function is to make these concepts, which are not otherwise derived from experience, serviceable for experiential use. For how would we procure sense and significance for our concepts if we did not underpin them with some intuition (which ultimately must always be an example from some possible experience)? If from this concrete act of the understanding we leave out the association of the image – in the first place an accidental perception through the senses – then what is left over is the pure concept of understanding, whose range is now enlarged and contains a rule for thinking in general. It is in just such a way that general logic comes about; and many heuristic methods of thinking perhaps lie hidden in the experiential use of our understanding and reason; if we understood how to extract these methods carefully from that experience, they could well enrich philosophy with many useful maxims even in abstract thinking.

Of this kind is the principle to which the late Mendelssohn expressly subscribed for the first time, so far as I know, in his last writings (the Morning Hours, pp. 164–165, and the Letters to Lessing's Friends, pp. 33 and 67): namely, the maxim that it is necessary in the speculative use of reason (which Mendelssohn otherwise trusted very much in respect of the cognition of supersensible objects, even so far as claiming for it the evidence of demonstration) to orient oneself by means of a certain guideline which he sometimes called common sense or healthy reason (in the Morning Hours), and sometimes plain understanding (To Lessing's Friends). Who would have thought that this admission would not only have a destructive effect on his favorable opinion of the power of speculative reason when used in theological matters (which was in fact unavoidable), but that even common healthy reason, given the ambiguous position in which he left the employment of this faculty in contrast to speculation, would also fall into the danger of serving as a principle of enthusiasm in the dethroning of reason?