《道德形而上学基础·序言》第4节
A metaphysic of morals is therefore indispensably necessary, not merely for speculative reasons, in order to investigate the sources of the practical principles which are to be found a priori in our reason, but also because morals themselves are liable to all sorts of corruption, as long as we are without that clue and supreme canon by which to estimate them correctly. For in order that an action should be morally good, it is not enough that it conform to the moral law, but it must also be done for the sake of the law, otherwise that conformity is only very contingent and uncertain; since a principle which is not moral, although it may now and then produce actions conformable to the law, will also often produce actions which contradict it. Now it is only in a pure philosophy that we can look for the moral law in its purity and genuineness (and, in a practical matter, this is of the utmost consequence): we must, therefore, begin with pure philosophy (metaphysic), and without it there cannot be any moral philosophy at all. That which mingles these pure principles with the empirical does not deserve the name of philosophy (for what distinguishes philosophy from common rational knowledge is that it treats in separate sciences what the latter only comprehends confusedly); much less does it deserve that of moral philosophy, since by this confusion it even spoils the purity of morals themselves, and counteracts its own end.
注释摘要
在这一段里，康德为他整本书的计划给出了一个直接的辩护：为什么必须建立一门道德形而上学。他提了两个理由，一个是理论上的，一个是实践上的，而第二个理由才是他真正着力的地方。 从理论上看，道德形而上学之所以必要，是因为我们要追问那些先天地存在于理性之中的实践原则到底来自哪里。这是一种思辨的兴趣，指向的是对理性自身能力的考察。但康德立刻说，这不是唯一的原因，甚至不…