The simplest form of the moral argument is as follows:
This is a deductively valid argument, which is to say if its premises are true its conclusion cannot be false. The key question is whether or not the premises are true.
The first premise is by far the most often-disputed premise in the argument. While many religious believers take the first premise for granted, the reasons for thinking it true are not clear, and there are some serious objections to it.
Arguments for the first premise
Famous atheists rejected morality
Though this line of argumentation is popular among religious apologists, it clearly commits the fallacy of appealing to authority, and that is not its only problem. Many nontheists who have rejected conventional views of morality have done so on grounds independent of their views on the existence of God. Also, it requires selectively quoting authorities, because many nontheists--indeed, many theists--have rejected the first premise of the moral argument. Finally, it is trivially easy to construct a similar argument against theism, for example: "John Calvin did not believe in free will, therefore 'If God exists, free will does not exist,' but free will does exist, therefore God does not exist." Even if Calvin had good arguments for his stance on free will being entailed by theism, non-Calvinistic theists will not be swayed by the mere citation of Calvin's authority, nor should they be.
Hitler and Stalin were atheists
Main article: 20th century atrocities
The basic fallacy of this argument is similar to the one in the first, though it could be considered an example of guilt by association rather than an appeal to authority. Furthermore, the historical accuracy of the argument can be questioned. Hitler's theistic proclamations are well documented, and anti-religious quotes attributed to him are apparently inauthentic. He seems to have held to basic doctrines of Christianity, in spite of rather unorthodox changes, such as his belief that Jesus was an Aryan and Paul corrupted Christianity with proto-Bolshevism. Stalin was an atheist, but given that this is one of many beliefs he held, it is unclear why his actions should be attributed to his atheism. For example, though many would be surprised by this, Stalin opposed mainstream theories of evolution on the grounds that they were too capitalistic. Stalin's rejection of evolution could just as easily be named the source of his crimes as his rejection of God, and indeed his rejection of evolution arguably sheds more light on the ideological dogmatism at the heart of the Soviet regime.
If God does not exist, humans are just animals
One snappy response to this argument is "Humans are animals whether or not God exists," which has indeed been the consensus view among taxonomists since Aristotle. Though this point may seem trivial, beneath it is the deeper point that it is hard to see how God's existing or not existing changes the status of humans. If the theist insists on claiming that human beings are worthless on their innate attributes alone, it is hard to see how God could change this situation; see Appeal to emotion. It also rests on the assumption that animals do (or would) not have any sort of relationship with or ability to worship a god. While this may be the case, we do not and can not know this for certain. The truth is however that humans are animals, and just because this fact may not be liked by some does not make it any less true. In addition one could ask “so what? Why presuppose that being an animal is a bad thing?”
Moral law requires a Lawgiver
Though we sometimes use the same words to talk about moral principles and human legislation, closer inspection calls into doubt the claim that there is a strong analogy between them. Human laws can be changed if the government wills it and follows correct procedures, but moral principles are typically thought to be unchanging. Also, it is possible to have a bad human law, but it is impossible to have a bad moral principle. In response to this second argument, it could be claimed that amoral laws are analogous to acts of a lower body that violate acts of a higher body which the lower body is responsible. This seems intuitively wrong, however: the wrong in a national law relegating part of the population to sub-human status seems very different, and more serious, than the wrong in a local law that contradicts a state. This argument is built on an equivocation, and is fallacious on those grounds.
God's rewards and punishments needed to make morality in one's own self interest
Usually, this argument is not stated so baldly. A more typical statement is "we admire people who sacrifice their lives for others, but if there is no God who rewards self-sacrifice, then such people are being stupid." When the underlying assumption is stated explicitly, most people recoil. Most people do not believe that the ultimate maxim by which we should act is "look out only for your own self interest." Though such a view is technically an ethical theory (known to philosophers as ethical egoism), it is not what most people mean when they talk about morality. It seems that if ethical egoism is true, then the second premise of the moral argument is false, at least in the normally understood sense.
Absolute morality requires an absolute standard
Statements of this argument are often unclear, but it seems to rest on an equivocation of the term "absolute," in much the same way that the Lawgiver argument rests on an equivocation of the term "law." The two relevant senses here are "applicable in all cases" (a characteristic typically applied to moral principles) and "omnipotent, omniscient, etc." (a characteristic typically assigned to God). There is no reason to think that the first sense entails the second sense.
Arguments against the first premise
Circular definition/no definition of "moral"
A common understanding of "moral" is assumed - why? The word "moral" should be defined as soon as it's introduced - this definition can't include reference to a god without the argument becoming circular, and if it doesn't include reference to a god, then in what sense is a god necessary for the concept?
For example, why does the apologist consider rape to be wrong (assumning they do)? "It is contrary to God's nature" is begging the question; "because the victim suffers needlessly" would require subsequent proof that the victim wouldn't suffer in a godless universe. ("There wouldn't be a universe at all without a god" and the argument folds into First Cause et al.)
The Euthyphro dilemma
This is perhaps the most famous objection to the second premise. The Euthyphro dilemma is found in Plato's Euthyphro, in which Socrates asks the question, "Is the pious loved by the gods because it is pious, or is it pious because it is loved by the gods?" In layman's terms this would be, "Is that which is good commanded by God because it's good, or is it good because God commands it?" Both options are problematic for those who would claim morality is dependent upon God.
If God is free to decide what is good, and it is good by virtue of his decree, then God has no higher standard to answer to. Therefore his will may be seen as genuinely arbitrary. Although God once decreed that murder and theft are morally wrong, he might have declared the opposite just as easily, so then murder and theft would be right. This makes morality arbitrary, not what most theists mean to say in articulating the second premise of the moral argument.
If right and wrong are inherent to the action, regardless of God's decree, then God has nothing to do with the process. God doesn't set moral standards; he follows them, and is therefore irrelevant to morality (except to the extent that he can tell us things which we could not figure out for ourselves.)
If goodness is not something that a god exhibits, but something of which the god is the source, the statement "god is good" becomes a meaningless tautology. Consider the property "tastes like an apple". Many things that aren't apples exhibit this quality, but what does it mean to say that an apple tastes like an apple? Nothing; it simply cannot be any other way. Similarly, defining god as the source of the property "goodness", then applying that property back to god, is equivalent to saying "god is consistent with his own nature", which tells us nothing.
An effective summary of the argument was given by Bertrand Russell:
"The point I am concerned with is that, if you are quite sure there is a difference between right and wrong, then you are then in this situation: is that difference due to God's fiat or is it not? If it is due to God's fiat, then for God himself there is no difference between right and wrong, and it is no longer a significant statement to say that God is good."
One perceived way to get out of the dilemma is to say that, although God has the freedom to command immoral acts such as rape, he would never do such a thing because it goes against his character or nature.
In response, Michael Martin has argued that this doesn't solve anything because the dilemma can be reformulated in terms of God's character: "Is God's character the way it is because it is good or is God's character good simply because it is God's character?" The structure of this modified dilemma is exactly the same as before, and it appears to be if anything harder to escape.
Another counter to ED is to take "good" outside the scope of command/endorsement and tie it to god's nature, as in "it is in god's nature that murder is wrong". However, the nature of X is intrinsic, applying only to X. "It is diamond's nature to be hard" is only meaningful when diamond's scratching other materials is being considered, and it is meaningless otherwise; diamond's hard nature has nothing to do with sapphire scratching quartz, for example. A theistic god is separate from the universe, so if Dave murders John, how can god's nature have any bearing on the situation?
Moral truths as necessary truths
Richard Swinburne, a theistic philosopher, has argued that moral truths cannot depend on God because moral truths are necessary truths, existing in all possible worlds, including ones where God does not exist. This objection of Swinburne's was cited by Jeffery Jay Lowder in Lowder's debate with Phil Fernandes. Keith Yandell, another theistic philosopher, raised a similar objection in his comments on the Craig-Flew debate.
- Main Article: Which God?
This argument does not specify a particular God which is the source of a true objective moral standard. Even if one accepted the argument, one would be forced to decide which religion to follow by some other means. If one can determine which God is the "true" God without using this argument, how is the argument necessary in the first place?
Alternatively, if one cannot rationally find the correct religion, the argument undermines its own respect towards objective morality, by suggesting that morality comes from a source we cannot recognize. While this does not mean that the argument is false, it does imply that human beings can never legitimately understand whether they are acting rightly or wrongly.
Incidentally we can also ask, Which morality? Christian morality changes with history and varies according to which Christian individual or which Christian sect is interpreting Christianity.
Many atheists like to state that they are technically naturalistic pantheists, meaning that they believe that God is the universe, but in a way that rejects supernatural or paranormal elements.
Based on this, one can assert that there is, in fact, a Godly morality, but that the definition of God is the natural universe, and, therefore, morality is both objective and superior to human morality.
Argument is self-refuting
One can argue that if God does not exist, an objectively provable existence of objective morality does not exist, and an objective need for objective morality to exist does not exist. Hence, the atheistic situation is no longer problematic.
The argument boils down to "objective morals exist, therefore god exists". Thus, the proposed definition of "moral" must simultaneously OMIT god (so the argument isn't circular, god being the conclusion) and REQUIRE god (in order to reach the conclusion at all). This is logically impossible.
Another way to look at it is, regardless of whether or not the premises have/require god or omit god, the argument is doomed to fail. If the premises have god in the sense of a being then the argument is circular, if the premises have god as a concept or omit god then the argument is invalid:
If the premises have god (the being) then the argument becomes circular because god the being, what the argument is trying to prove, is assumed as a premise.
If the premises have only the concept of god and not the being god, then the argument becomes an invalid argument of false equivocation. The premises have god in the sense of a mere concept, and the conclusion has god in the sense of an actual being. The two are not equivocal. For example the mere concept of a dragon is not equal to a real dragon. So no matter what the premises prove about the concept of god, it would not necessarily follow from those premises that there is an actual god. In other words, it is possible for the premises to prove something about the concept of god and thus be true but it can still be false that god as an actual being exists.
If the premises have nothing to do with god, then the argument has no validity because god is not a valid inference from the premises.
Argument from Ignorance
The moral argument is also one from ignorance. Even if objective moral values and duties were proven to exist 100%, it doesn't follow that a god put them there. It may, for all we know have been aliens who put them there. Just because we don't know where morality came from, doesn't mean we should presuppose a god did it. This argument, in some ways therefore falls under the same category as the Teleological and Cosmological arguments.
Heaven precludes genuine charity
If there is an omnipotent and perfectly just God and an everlasting reward, there is no reason to act morally except to secure one's own well-being in the afterlife, i.e. loving your brother can only be a rational means to one's own ends not the well-being of one's brother.
- If all else being equal my actions cause you to forego a good I have wronged you.
- Heaven is a good that outweighs all Earthly goods.
- In a perfectly just world, any wrong done to a person that can be compensated will be compensated.
- God desires a perfectly just world.
- God is omnipotent, therefore capable of compensating any wrong.
- If my actions caused you to forego Heaven (for example by convincing you to reject God or seeing that you die before repenting) you would be wronged. (Premises 1, 2)
- God desires to compensate any wrong. (Premises 3, 4)
- God would compensate you for that wrong. (Premise 5, Argument 2)
- No action of mine can deny you a good that makes all others trivial or otherwise affect your ultimate well-being. (Arguments 1, 3)
- No action of mine can deny you Heaven or otherwise affect your ultimate well-being. (Permise 2, Argument 4)
My actions are irrelevant to your ultimate well-being (Argument 5) assuming a just God and an eternal reward (Premises 1-5).
- Main article: Secular morality
Finally, it can in general be claimed that there is a specific, well-founded theory of morality that leaves God out of the picture. This is a complex topic and is dealt with in full by the above-linked article. One thing is worth noting here: some theists appear to think that it constitutes a valid link in the moral argument to simply demand a secular theory of morality without giving any reason to think that theistic theories are more likely to be successful. This is clearly fallacious, and debaters should not fall into this trap. Meta-ethics, like most areas of philosophy, has unresolved debates, but pointing to an unresolved philosophical debate is no argument for the existence of God. To show that the moral argument is unsuccessful, one need only show that we should not accept the second premise. Full development of secular theory of morality may be helpful here, but it is not necessary.
Other formulations of the moral argument
Normativity of morality
This formulation of the moral argument relies on the assumption of normativity, that is to say, that the awareness of morality is a more or less universal experience among humans. Most people recognize that, for example, murder is wrong. From there, a theist claims that this universal awareness must come from some ultimate source, which is God. 
To put it concisely:
- It appears to human beings that moral normativity exists.
- The best explanation of moral normativity is that it is grounded in God.
- Therefore God exists.
This version of the moral argument may sometimes be used by theists as red herring when responding to arguments about the moral nature of God. For instance, a person who points out the inherent cruelty of exterminating 99% of the earth's population, as in the story of Noah's ark, or takes issue with the apparent Biblical support of slavery and rape, may quickly expect to be countered with this claim:
"You recognize mass murder/slavery/rape as a bad thing, so you must have some standard to judge that against. If there was no God, then you'd have no rational reason to say that those things aren't good."
Counter-apologetic responses to normativity
- Although the awareness of SOME sort of right and wrong is apparently universal, many specific details differ across cultures and time periods. In the case of slavery, for example, the practice was once universally accepted in the southern United States, and many anti-abolitionists even quoted the Bible to justify the practice. (See the main slavery article for more details.) This indicates that morality has a strong cultural component to it, and is tied up in evolving notions of secular morality.
In fact, this serves as an argument against the existence of God.
A recently proposed atheological argument is the Moral-Knowledge Argument, which can be expressed as follows: If the theists' version of god exists, then he is a being who is omnipotent, omniscient, and benevolent. Since this god is benevolent and his ethics are supposedly morally good for humanity, he would want all human beings to know his ethics perfectly. And since this god is omnipotent, it would be within his capacity to make sure that all human beings know his ethics perfectly. However, all human beings do not know his ethics perfectly, which is shown by their disagreeing about many moral values. Therefore, this version of god does not exist.
- Other human perceptions also have the appearance of being normative. For instance, most people agree that chocolate is "delicious," while dirt is "not delicious." By the same reasoning as the argument from normative morality, it could be said that there must be some ultimate standard for deliciousness, and that standard must be God, the ultimate tasty treat. We could use a similar argument to prove that God is the definition of the perfect homosexual lover.
- The fact that there may be an abstract standard of perfect goodness that an individual strives to achieve, does not indicate that this standard represents an existing object. For example, golfing a perfect game would yield a score of 18. However, even though no one in history has ever golfed an 18, this is the the best attainable score according to the rules of the game. It is quite possible to have a theoretical ideal, yet not have any concrete instance of that ideal. Therefore, we could say: "Yes, this thing that you call 'God' could be our standard for morality. However, this tells us nothing about whether or not God exists."
The Immoral Imperative
- Christians are called to evangelize and share the gospel as a command from God. The mercy of God is shared for the purpose of conversion which treats people as a means. According to Kant, treating anyone as a means rather than an end in themselves is immoral, therefore, Christians are immoral as is the command.
A possible solution to this dilemma is in reassessing the command from God. If the gospel of Christianity is not specifically for the sake of the gospel itself, nor is it a means to God's end, but rather is the means by which a person's life is improved, the individual becomes the end, thus making it moral under the Kantian mindset. The person "receiving" the evangelism (i.e. the gospel) is treated justly insofar as her personal improvement is the goal. This solution can only be upheld if the reality of "salvation" is in fact the reality of a better life.
- ↑ C. S. Lewis, Mere Christianity, 1943, Chapter 1
- Stan W. Wallace, ed. Does God Exist?: The Craig-Flew Debate. Ashgate, 2003.
- Richard Swinburne. The Existence of God. Oxford University Press, 2004.
- Richard C. Carrier. 'Hitler's Table Talk: Troubling Finds.' German Studies Review 26.3 (Oct 2003): 561-76.