《道德形而上学基础·第三节·从道德形而上学过渡到纯粹实践理性批判》第15节
The subjective impossibility of explaining the freedom of the will is identical with the impossibility of discovering and explaining an interest which man can take in the moral law. Nevertheless he does actually take an interest in it, the basis of which in us we call the moral feeling, which some have falsely assigned as the standard of our moral judgement, whereas it must rather be viewed as the subjective effect that the law exercises on the will, the objective principle of which is furnished by reason alone. [Kant's note] Interest is that by which reason becomes practical, i.e., a cause determining the will. Hence we say of rational beings only that they take an interest in a thing; irrational beings only feel sensual appetites. Reason takes a direct interest in action then only when the universal validity of its maxims is alone sufficient to determine the will. Such an interest alone is pure. But if it can determine the will only by means of another object of desire or on the suggestion of a particular feeling of the subject, then reason takes only an indirect interest in the action, and, as reason by itself without experience cannot discover either objects of the will or a special feeling actuating it, this latter interest would only be empirical and not a pure rational interest. The logical interest of reason (namely, to extend its insight) is never direct, but presupposes purposes for which reason is employed.
注释摘要
这段论证处理的，是全书走到尾声时一个无法回避的尖锐问题：就算我们承认自由是道德律的前提，人凭什么要关心这个律，是什么让我们对道德律本身产生兴趣。康德把这个问题的不可解释性，直接等同于自由意志的不可解释性。这不是在回避，而是在划定界限。 要理解这一步，先得抓住康德在这个地方对“兴趣”这个词的特殊用法。在正文夹注里他给了明确界定：兴趣是使理性成为实践的、也就是…