Commentary on the preface to the Metaphysics of Morals – Tristan Stone

PREFACE

“Everyone must admit that a law, if it is to be valid morally, i.e., as the ground of an obligation, has to carry absolute necessity with it; that the command ‘You ought not to lie’ is valid not merely for human beings, as though other rational beings did not have to heed it; and likewise all the other genuinely moral laws; hence that the ground of obligation here is to be sought not in the nature of the human being or the circumstances of the world in which he is placed, but a priori solely in concepts of pure reason, and that every other precept grounded on principles of mere experience, and even a precept that is universal in a certain aspect, insofar as it is supported in the smallest part on empirical grounds, perhaps only as to its motive, can be called a practical rule, but never a moral law.”

Here, Kant is arguing that, by their very nature, morals imply a duty – it is not only what one does when no one else is looking but what one ought to do. 

…all moral philosophy rests entirely on its pure part, and when applied to the human being it borrows not the least bit from knowledge about him (anthropology), but it gives him as a rational being laws a priori, which to be sure require a power of judgment sharpened through experience, partly to distinguish in which cases they have their application, and partly to obtain access for them to the will of the human being and emphasis for their fulfillment, since he, as affected with so many inclinations, is susceptible to the idea of a pure practical reason, but is not so easily capable of making it effective in concreto in his course of life.

An essential part of Kant’s thesis is that ethics must rest upon a priori synthetic judgments. The laws themselves are to be worked out a priori but we need experience to know which laws to apply when, as we are creatures of emotions and it’s difficult to actually live by it. 

…For as to what is to be morally good, it is not enough that it conform to the moral law, but it must also happen for the sake of this law;

Again, Kant’s emphasis on duty to the moral law is of paramount importance.  We must not simply act in agreement with the moral law but out of a duty to it – i.e. because we feel our obligation to conform to the moral law.  Again, the question should be: “what does the moral law compel me to do?” or “what should/must I do?”

The present groundwork is, however, nothing more than the search for and establishment of the supreme principle of morality, which already constitutes an enterprise whole in its aim and to be separated from every other moral investigation.

Kant explicitly tells the reader this is something of a prolegomenon – or introduction – to a longer, more detailed work to follow and that its purpose is to find the essential and supreme principle of morality [the categorical imperative].