A charge that’s often leveled at atheists is that their position encourages moral relativism. Only religion can provide us with morality or ethics that is firm and stable, the charge continues, because, after all, religion rests ethics or morality on God’s word.

Yet the very opposite is the case. In America alone there are some 4200 different religions and while many differ from each other minimally, if there are but 20 doctrines that are seriously distinct in what they preach, that is quite enough to promote the idea that what is right for human beings to do is highly varied. Roman Catholics differ significantly from Muslims, Methodists from Hindus, and Jews from the Pentecostals concerning what is most important for us to do. Just consider that some religions claim that abortion is out-and-out murder at every stage of the development of the fetus, while others hold that this is quite wrong and abortion is homicide only after, say, the 24th week of pregnancy. Some religions teach pacifism while others consider self-defense morally justified—and their theory of warfare reflects this and produces very different practical judgments as to the international policies of the world’s countries.

None of this should be surprising. Faith-based moralities are impossible to ground on anything solid. The Bible, for example, is filled with reports by certain prominent faithful disciples and “witnesses” concerning God’s proclamations; the Torah and the Quran are in the same fix. The implication is clear: religious ethics or morality produce very different principles by which human conduct is to be guided in all its enormous variety. No single principle is necessarily shared, nothing is solidly grounded because it all rests on acts of faith, commitments that are without a factual and mutually ascertainable basis. Unlike science—wherein even while there’s considerable argument and lack of conclusiveness, the idea is that with close attention and careful study, there is no such thing as varieties of biology, chemistry, or physics—in religion, based on faith, disagreements are inherent, nearly unavoidable. (I will ignore here the occasional philosophically defended relativism some claim for the sciences.)

In short, science has an overarching premise to seek out truths through close observation and study, and this holds for all disciplines, including biology, chemistry, and physics. Common sense and its more developed version, science, can reasonably promise a common basis for how human beings ought to conduct themselves. Secular philosophies, such as those advanced by Socrates, Aristotle, Spinoza, Hobbes, Hume, and others, purport to find common ground for answering ethical or moral questions in certain factual realms such as biology, history, psychology, sociology, economics, and so forth.

From the beginning of elaborate discussions of ethics, secular approaches have held out the promise of finding a basis for guiding human conduct in, for example, an understanding of human nature. Not that these have been fully successful or triumphant but that is not the issue here. The point is that when one rests ethics or morality on facts—and let’s ignore for the moment Hume’s so called “is-ought” gap, which is widely misunderstood (for Hume “ought” cannot be deduced from “is” but there may well be other rational ways to derive or infer “ought” judgments from knowledge of what “is” the case)—there is greater likelihood that common understanding can be achieved than if faith is proposed as the basis.

Our common sense, too, backs up this assessment. It is pretty certain that we know the difference between human beings and other animals. Anthropologists, for example, have no trouble telling who are the people as opposed to non-human animals in various regions of the globe. Nor do ordinary folks.

It is for this reason that there can be organizations such as Amnesty International and Human Rights Watch, which tend to agree on certain basic principles or at least hope to do so in time, based on what they know about human beings. Just as Socrates, Aristotle, Spinoza, and others thought an understanding of human nature would provide the basis of the moral virtues we ought to practice, so secular moral thinkers today hold out strong hope that careful study will provide a basis of judgments about right versus wrong in personal, public, and international affairs.

Of course, there are secular thinkers who deny that there is anything like ethics or morality to be found by studying the facts of human nature. Nevertheless, most of them maintain, with considerable plausibility, that the source of ethics or morality—as well as political principles, principles of justice and so forth—can only be human knowledge of various facts of reality and not something as elusive as religious faith which is sure to produce moral relativism.