Worthiest friend,

I have made you wait a long time for a response to your letter of December 9 of last year, but it is not my fault. For pressing labors hang about my neck and my age imposes on me a necessity I would not otherwise feel, to devote my thoughts to the project before me until I am finished with it. I must not let anything alien interrupt my thinking, for once I let go of the thread, I cannot find it again.

You have presented me with your thorough investigation of what is just the hardest thing in the whole Critique, namely, the analysis of an experience in general and the principles that make experience in general possible. – I have already made plans for a system of metaphysics to handle this difficulty and to begin with the categories, in their proper order (having first merely expounded, without investigating their possibility, the pure intuitions of space and time in which alone objects can be given to the categories); and I would demonstrate, at the conclusion of the exposition of each category (for example, Quantity and all predicables included under it, along with examples of their use), that no experience of objects of the senses is possible except insofar as I presuppose a priori that every such object must be thought of as a magnitude, and similarly with all the other categories.