Why should I be moral? One answer is that if we are moral, the gods will reward us; and if not, the gods will punish us. This is called “the divine-command theory.” (DCT) According to DCT, things are right or wrong simply because the gods command or forbid them, there is no other reason. (This is like a parent’s who says to a child: it’s right because I said so!)
To answer the question of whether morality can be based on a god we would have to know things like: 1) if there are gods; 2) if the god we believe in is good; 3) if the gods issue commands; 4) how to know the gods’ commands; 5) if we found the commands—say in a book—how would we know the commands are good ones; 6) if they were good commands how would we understand or interpret them; 7) if the came from a book which translation of the book; 8) how could you know if the translation is accurate; 9) can any translation be accurate; and 10) even if the translation was accurate how would you interpret the words you read. This is just a partial list of the problems you encounter trying to base ethics on a god or religion.
Difficulties also arise if we hear voices commanding us, or we accept an institutions’ authority. Why trust the voices or authorities? And which institution? Which revelation? Obviously, there are enormous philosophical difficulties with basing ethics on religion.
But let’s say that there are gods, that you have found the right one, that the right one issued commands, that the commands are good, that you have access to the right commands (because you found the right book, church, or had the right vision), that you understand the commands, that you interpret the commands correctly even though they came from a book that has been translated from one language to another over thousands of years? (Anyone who has ever translated knows that you can’t translate word for word between languages.) But let’s just say that somehow you are right about everything. Can you then base ethics on religion?
More than 2,000 years ago Plato answered this question in the negative. In Plato’s dialogue Euthyphro, Socrates asked a famous question: “Are things right because the gods command them, or do they command them because they are right?” If things are right simply because the gods command them, then their commands are arbitrary—without reason. There are no good reasons for their commands. The gods then are like petty tyrants who just command things because they have the power.
On the other hand, if the gods command things because they are right, then there are reasons for their commands. The gods command things because they see or recognize that certain commands are really good for us. But if that is the case, then there is some standard or norm or criteria by which good or bad are to be measured. And this standard is independent of the gods.
So either the gods command are without reason, and therefore arbitrary, or they are with reason, and thus are commanded according to some standard. This standard—say that we would all be better off—is thus the reason we should be moral. And that reason, not a god’s authority—is what makes something right or wrong. And the same is true for an authoritative book. Something is not wrong simply because the book says so. There must be a reason for this and if there is not, then the book is simply wrong.
Of course one could argue that even if the gods are petty tyrants who command us without reason—except for say their own amusement—we should still follow the commands so as not to suffer—since the gods are possibly powerful and mean enough to do so. If they can inflict eternal torture—if they are the ultimate sadists—then we do have a reason to follow their commands—to avoid torture!
The response to this is that we don’t know that the gods will reward us for following their non-rational commands. Maybe the gods reward people who use their reason and don’t accept such commands and punish those who are so frightened as to accept non-rational commands. This seems to make some sense, if the gods are petty, tyrannical bullies, they might like it if you stood up to them. Who knows?
The foregoing discussion should suffice to show how difficult it is to base ethics on religion. Again, even if one could overcome all the practical difficulties involved in philosophically justifying religion, it seems that either a) the gods commands are arbitrary and there is thus no reason to follow them; or b) the gods commands are not arbitrary and there are reasons for them. But if the latter is the case, then we are doing philosophical, not theological, ethics. We are looking for the reasons why things are moral or immoral.
Finally, you might object that the gods have reasons for their commands, and we just can’t know them. But if this is the case, if we really can’t know anything about the gods’ reasons, if the ways of the gods “are mysterious to humans,” then what’s the point of religion? If you can’t know anything why the gods command things, then why follow their commands, why have religion at all, why listen to the preacher? If it’s all a mystery, then no person or book or church has anything coherent to say about god, ethics, or anything else. and in that case you should just be a skeptic.
If we want to rationally justify morality, then we will have to do it in a moral theory independent of hypothetical gods. We will have to engage in philosophical ethics.