The trouble with acting solely on the basis of natural incentives like sympathy is therefore this. The maxims which are guiding our actions are derived from desires which aren’t shared by all (possible) rational beings, and thus can’t be regarded as expressions of pure moral reason. ¶ Why does Kant adopt this position? A person’s emotions, feelings, and inclinations are part of his or her biological inheritance. However admirable they may be, acts that are only expressions of feeling and inclination are acts of human animals, of beings caught up in the web of nature, locked into the system of natural causes and effects. When we act because we see that something is right, however, our behavior is an expression of our reason and will, of those aspects of ourselves which transcend nature. ¶ Two “worlds” or realities must be distinguished. The phenomenal world or world of appearances discloses itself in sense perception and is investigated by science. It includes observable substances, qualities, and events, and theoretical entities like subatomic particles which science postulates to explain them. “Behind” the world of appearances lies the noumenal world — reality as it is in itself, and not as it manifests itself to us. This world is inaccessible to theoretical reason and is therefore, in the strict sense, unknowable. But human beings belong to both worlds. As parts of nature, we are members of the phenomenal world, and our behavior can be explained in terms of natural causality. As free and rational beings, we are members of the noumenal world, and our actions are self-determined.

Despite the theological and popularly conceived connections between religious devotion and moral living, the difficulties attending theological or religious ethics — the attempt to tie ethics to theology or religion in some important sense — are myriad. Thanks largely to Enlightenment thought, morality has come to be construed as independent of God so much so that the majority of moral philosophers today would without without hesitation affirm that even if God exists, morality can exist apart from God — an ontological critique — and, if the precepts or dictates of morality can be known at all, they can be known apart from religious orthodoxy or theological reflection — an epistemological critique. ¶ Since the Enlightenment, at least, and in particular since Kant’s epistemological dualism, questions of religion and “speculative metaphysics” have often been considered beyond the ken of rationality. Kant’s motivation, it has been suggested, was to spare religion from the rigorous scrutiny of the emerging science of his day; but the actual result proved to be detrimental to religious conviction, for it began to be portrayed as an inescapably subjective affair. Universal truth claims became harder to reconcile with this kind of epistemology, which is likely the inevitable while paradoxical effect of implicitly putting religion and science at odds. Religious truth claims tend to be increasingly construed as devoid of propositional content and rational evidence and are instead seen as empty faith claims rooted in a person’s imagination or a group’s collective psyche.

The Darwinian argues that morality simply does not work (from a biological perspective), unless we believe that it is objective. Darwinian theory shows that, in fact, morality is a function of (subjective) feelings; but it shows also that we have (and must have) the illusion of objectivity.

How should one live? There are few questions, I think, that are as gripping and as inescapable as this one. Unlike many of the other classical questions of philosophy, this question — the central question of moral philosophy — seems pressing and important. It matters what answers we come up with, for it matters what I do with my life. What I make of myself, how I live, what I do, what kind of person I become — these things are of vital concern to each of us, even if few of us normally reflect on them in a systematic or critical fashion.

The position we have arrived at is this: in defending a moral theory, we must see how well that theory fits in with a wide variety of judgments that we are inclined to make about many different matters. We have opinions about cases, about principles, about the nature of morality, about what counts as an adequate explanation, and more. Some of these opinions are fairly specific, others are more general; some are arrived at rather "intuitively" and spontaneously, others only after considerable reflection; some are extremely difficult to give up, others are more easily abandoned. We try to find the moral theory that provides the overall fit with this eclectic set of beliefs. But if — as seems overwhelmingly likely — no theory can actually accomodate all of the relevant initial beliefs, we revise the set: we alter our beliefs, and reevaluate our theories, until we arrive as best we can at a theory that seems on balance to be more plausible than any of its rivals. Ultimately, then, defending a normative theory is a matter of arguing that it provides the best overall fit with our various considered judgments.

[J]ust as there was no guarantee at the beginning of cosmological and scientific speculation that we humans had the capacity to arrive at objective truth beyond the deliverances of sense-perception — that in pursing it we were doing anything more than spinning collective fantasies — so there can be no decision in advance as to whether we are or are not talking about a subject when we reflect and argue about morality. The answer must come from the results themselves. Only the effort to reason about morality can show us whether it is possible, whether, in thinking about what to do and how to live, we can find methods, reasons, and principles whose validity does not have to be subjectively or relativistically qualified.

If God is the basis of moral values, then such values must be objective, and we are, therefore, faced with the following questions: (1) How do we come to be aware of these moral values, if they exist entirely independently of us? (2) Why do moral facts supervene on natural facts? (3) How can the existence of objective moral values be reconciled with the existence of different conceptions of what is right. These difficulties are not faced by the atheist.

But, for the evils of which you complain, you have provided a singular remedy. Many, however, will think it too desperate, to be adopted without hesitation. To give stability to "staggering incredulity," you advise us to cut off, at one stroke, all that has been held venerable and sacred for ages; but, unfortunately, you have nothing to offer in its stead, but a liberation from every restraint on those unhallowed passions of our nature, which would furnish a passport to every vice. To remove doubts, you teach us to disbelieve; to promote the interests of moral virtue, you recommend: the abolition of every moral principle; and to awaken us from the delirium of superstition, you administer an opiate, which, while it cherishes the moral depravity of the heart, strangles, in the birth, every pang of conscientious remorse.