Ancient Greek philosophy was divided into three fields: logic, physics (natural philosophy), and ethics (moral philosophy). This division makes sense: Logic is the study of pure thought, independent of any objects. Physics is the study of how things happen in the world of material objects. Ethics is the study of how things ought to happen in the world of human beings.
Philosophy may also be divided on the basis of whether it is "pure" or "empirical." Pure philosophy deals only with a priori concepts; concepts that occur to us independent of any experience or perception. By contrast, empirical philosophy deals with the objects we experience in the world around us. Logic is pure philosophy as it relates to the formal procedures of thinking. "Metaphysics" is pure philosophy as it applies to our efforts to understand the world. Physics and ethics have both empirical and metaphysical branches.
Our task in this book is to develop a "pure" moral philosophy, a "metaphysics of morals" that relies on the a priori concepts of reason, not on empirical observations. That such a philosophy should be possible is apparent from the fact that we presume that moral obligations are binding not just for particular people in particular circumstances, but rather for all rational beings in all places at all times.
In their daily lives, people must apply moral laws to many different situations and circumstances. Developing a clear understanding of moral principles can help people to keep track of their moral obligations. A clear understanding of morals can also help people to ensure that their motivations are pure. Actions are not truly moral if they only appear to conform to moral law but lack a moral motivation.
The goal of the Grounding for the Metaphysics of Morals is to establish the "supreme principle of morality." Kant intends to follow this work with a more thorough treatment of moral philosophy. The Grounding is meant to be more accessible than this later work.
The distinction that Kant draws in the Preface between "pure" and "empirical" concepts is of critical importance to his philosophy. "Pure" or "a priori" concepts are ideas that occur to us when we think about things in our minds, "prior" to and independent of any experience of how things happen in the world. "Empirical" or "a posteriori" concepts are ideas that we derive from our experience of the world.
In the Critique of Pure Reason, Kant argued that many of our basic ideas about the world--our notions of time, space, and causation, for instance--are a priori concepts; they are "hardwired" into our brains, rather than extrapolated from our experiences. This argument led him to a number of interesting conclusions about the limits of human understanding and the errors of traditional philosophy (see the Context section for more information on the first Critique). In this book, Kant makes a similar argument about moral philosophy. He identifies the basic principles of moral thinking that occur to us independent of any particular situation or experience, and he offers some criticism of philosophers who have advanced different bases for morality.
Kant argues that his project makes sense in terms of our intuitions about morality. About halfway through the Preface, he claims that when we think about morality, we naturally presume that moral laws must apply to all people at all times. He bases this claim on the notion that moral actions are supposed to be undertaken for the sake of morality alone; we are supposed to have pure (as opposed to self-interested) motivation for moral actions. Yet as soon as particular circumstances enter the picture, it becomes impossible to think of motivations being entirely pure; in any particular situation, human beings will have interests and concerns that form a component of their motivation.
This train of thought leads Kant to the conclusion that a secure understanding of morality must be based on the "pure," a priori concepts of reason. "Pure," a priori concepts are concepts that occur to us before we have any experience of the world. If moral ideas were drawn from experience, then they could not be assured universal validity, for they would be based only on the limited set of events that we have experienced. Moral ideas may be universally valid, Kant argues, only if they are based on the intrinsic validity of a priori concepts.
Kant's distinction between "rational beings" and "men" may make this point more clear. Being a human being entails possessing a certain "human nature." We get hungry, we fall in love, we have emotional and physical needs. In Kant's view, this human nature should not be a consideration in moral thinking. Human nature is a particular circumstance that affects human beings. We could imagine some other form of rational being--an extraterrestrial life form, for instance-- possessing a different nature. But we would not excuse the cruel behavior of some monstrous creature; rather, we would judge the monster's actions according to the same moral standard that we apply to ourselves. According to Kant, this fact demonstrates that our moral thinking is not based on an understanding of "nature" or disposition, but rather on universally applicable concepts--and the only concepts that we can know apply in all circumstances are the concepts that occur to us a priori, independent of any particular experience or circumstance.
You may be thinking at this point that Kant seems to want people to behave like robots. By his account, morality requires us to separate our rationality from our nature and act solely on the basis of logical principles. This idea is strongly rooted in the basic ideas of the Enlightenment (see the Context section for discussion of this period in European intellectual history). Like many of his contemporaries, Kant understands reason to be the source of fundamental truths that transcend culture and history. Rational ideas are ideas that makes sense to all people; they are universal. Kant believes the task of philosophy is to develop a stronger understanding of these ideas. He also believes that rational ideas have a strong claim to authority. A morality based on reason would make sense to all people; Kant thinks it would therefore be superior to a moral system accepted by only one particular group of people.
Critics of Kant have challenged his effort to develop a moral system based exclusively on reason. Some have argued that it is unnatural to reason about morals; in practice, we rely on intuition, rather than analysis, to determine what we feel is the moral course of action. Some have argued that it is impossible to separate rationality from nature and culture; what makes sense to us has a lot to do with ideas and prejudices that we learn from our parents and our communities. Some argue that Kant's idea that we should reason about morals is itself a cultural prejudice that doesn't make sense to people living at other times in other cultures.
On the other hand, we do tend to believe that certain basic moral ideas are based on something more than local cultural prejudice. To pick just one example, many people in the West think that basic human rights should be respected in all societies; according to this view, human rights transcend particular communities and apply in all places at all times. This way of thinking is strongly indebted to Kant and his colleagues in the Enlightenment.
Keep these issues in mind as you advance through the Grounding for the Metaphysics of Morals and evaluate Kant's argument. In the Preface, the only example Kant gives of a specific moral principle with universal validity is his comment that people should not lie. More examples and definitions about moral principles will follow in later chapters.
Note: Before continuing, a brief comment on Kant's gendered language is in order. In German there are two words corresponding to the English for "man": one for man in the sense of a male adult, and another for man in the sense of "mankind." Kant's use of the latter term is often translated simply as "man" or "men" in English. Arguably, it might be better translated as "human being" or "person." Kant certainly shared in the prejudices of his time regarding the intellectual capacities of women. Nevertheless, his language is not as sexist as it appears in some translations.