Can somebody tell me where this famous quote comes from?
I mean in which book and on which page. I want to find this in German. If someone can provide the quote in German the way Kant wrote it, I would be grateful!
It occurs in the Groundwork of the Metaphysics of Morals, here it is in context (from 4:418-19, p.29 in the Gregor's Cambridge translation):
"He is not capable of any principle by which to determine with complete certainty what will make him truly happy, because for this omniscience would be required. One can not therefore act on determinate principles for the sake of being happy, but only on empirical counsels [...] so that there can be no imperative with respect to it that would, in the strict sense, command him to what would make him happy; for happiness is not an ideal of reason, but of imagination, resting on merely empirical grounds, which it is futile to expect should determine an action by which the totality of a series of results in fact infinite would be attained."
The Role of Happiness in Kant’s Ethics by Hughes is a nice commentary. As can be seen from the quote, Kant's somewhat dim view of the prospects of happiness relies on his maximalism about knowledge that elevates "certain" a priori principles, and their implications, above the merely empirical claims. However, as we are no longer as confident of possessing any such "certainties" of reason, happiness may not, in principle, be in a worse position than anything else we pursue. Or at least a different argument would be required to the contrary.
Here is the German original of the quote above:
"[E]r ist nicht vermögend, nach irgend einem Grundsatze mit völliger Gewissheit zu bestimmen, was ihn wahrhaftig glücklich machen werde, darum weil hiezu Allwissenheit erforderlich sein würde. Man kann also nicht nach bestimmten Prinzipien handeln, um glücklich zu sein, sondern nur nach empirischen Rathschlägen [...], mithin kein Imperativ in Ansehung derselben möglich [ist], der im strengen Verstande geböte, das zu tun, was glücklich macht, weil Glückseligkeit nicht ein Ideal der Vernunft, sondern der Einbildungskraft ist, was bloß auf empirischen Gründen beruht, von denen man vergeblich erwartet, dass sie eine Handlung bestimmen sollten, dadurch die Totalität einer in der Tat unendlichen Reihe von Folgen erreicht würde."