What distinguishes moral rules from other arbitrary normative statements? Kant's moral law which states we should not use others merely as means to an end. This rule, how is it different from other arbitrary normative statements such as that you should not eat pork? How do you distinguish them? What features do you look at?
You don't make clear what distinction you are making between a 'moral law' and an 'arbitrary normative statement'. This could be taken several ways. What distinguishes arbitrary normative statements that are moral rules from arbitrary random normative statements that aren't? (Like 'Don't murder' versus 'Don't eat lemons on Tuesday'.) What distinguishes 'true' moral rules from 'false' ones? What distinguishes universal moral rules from local or temporary rules specific to an individual culture? What distinguishes rationally justified rules from unjustified ones? Given that, I can't tell what would answer the question.
Morality is a universal human instinct like language, and like language, has both universal and arbitrary aspects to it. Where language has evolved to enable social animals to communicate plans and intentions and thus work together cooperatively, morality has evolved to enable to live together in dense social groups, with overlapping territories and sharing resources, minimising conflict. Both are created jointly and collectively in social interaction - they only function if they're widely shared. We have a very strong urge to 'fit in' with the culture we're born into. Both are adaptive, allowing societies to adjust to a wider variety of circumstances.
So both have universal features, that are related to their evolutionary purpose. Moral systems pretty much all include rules governing property ownership, and resolving in-group conflict without violence. Where there are conflicting interests, they will generally take a side, and require one party to defer to the other. They will forbid behaviours that annoy, harm, or put at risk other members of the social group. They will often forbid acts that risk self-harm. They will also impose punishments on those within the group who break the rules, and recommend behaviours to exclude, resist, or take over those who are not members of the group. But they will also contain much that derives from historical accident, or rules in the private interests of the rulemakers, or that otherwise depends on the circumstances when the rule was made.
The ruling against eating pork, for example, has several possible origins. It has been suggested that because pigs are biologically so similar to humans we share a lot of the same parasites, and so eating pork could lead to illness. Another is that it simply codifies the instinctive 'disgust' reaction to foods we're not familiar with that was extant at a particular point in time. We learn what foods are good to eat from our parents as children - any food we haven't tried in early childhood subsequently evokes feelings of disgust. (Westerners don't like eating insects, but scampi is fine.) So it's a safety mechanism. But the most probable explanation is that it is like many Biblical rules - a proscription against the practices of pagan outsiders. Non-Jews ate pigs, and wore clothes of mixed fibres, and worshipped idols, so those were forbidden as a way of distinguishing members of the tribe from outsiders.
As with language, it is common for people who have only been exposed to one culture, one moral system, to assume it must be both universal and 'obvious'. The stereotype of the Englishman abroad who thinks he can make himself understood by speaking English very loudly and slowly is an old joke, but the same observation applies to morality, but with even more devastating effect. Genocidal wars are started when different moral systems collide. Moral rules we today think of as universal and obvious, history shows to be anything but. So for example, for most of human history we have practiced slavery. The pyramids of Egypt were built by slaves. The Bible tells of how Moses brought the Israelites out of bondage in Egypt, and then took slaves themselves as they invaded and destroyed the tribes of the lands they moved into. It was also practiced in the ancient cultures of Africa, India, China, the Middle East, Central America, and Europe. So Kant's rule "we should not use others merely as means to an end" is most definitely not universal. There have been (and still are) many moral systems that don't hold to it. Many countries still practice slavery and human exploitation even today. Many countries who do so think it is the West that is immoral, for not adhering to their mores. Like people who speak different languages, people of different moral systems are incomprehensible to one another.
So you can use evolutionary game theory to try to identify moral rules that are more likely to be 'universal' or 'true' because they serve the evolved purpose of enabling social cooperation. So for example, 'tit-for-tat' and 'forgiveness' have been shown to be sound strategies in game theory. But pretty much every moral rule has exceptions.
It is the nature of a normative rule to be a moral rule: both create a value structure that differentiates between 'right' action and 'wrong' action. And no rule is ever purely arbitrary. Rules are imposed for reasons. We might disagree with the reasons — think they are silly, dated, selfish, etc. — but our disagreement doesn't imply they are not factually reasons.
The rules we tend to view as 'moral rules' in the colloquial sense share a few characteristics:
- They are universals: meant to be applied by all people, to all people, in all contexts
- They are coherent: fitting and consistent within an overarching moral worldview
- They are reflexive: meaning they are applied to us by others in the same way that we apply them to others
Something like the proscription against eating pork may seem less like a moral rule than Kant's Categorical Imperative, but only because the first is universal solely within the Judaic and Islamic worlds, while the second is meant to be universal within any worldview. The more that rules are restricted in scope, the less overtly universal they seem; but within their proper scope they are still universals. Even something as trivial as the rules that govern the movement of chess pieces are technically moral rules within the extremely limited scope of the game of chess (and anyone who has played chess knows that breaking chess rules can produce something much like moral outrage from an opponent).
How can we tell what is moral?
By Conscience, which literally means "the knowledge with you". Conscience cannot be substituted by any algorithm and it cannot be explained away. All people have a Conscience.
What is moral is defined as what is consistent with Conscience. The Conscience can be searched, examined and applied to any circumstance. Often this highlights the need for additional knowledge of truth which, once gained, clarifies whether a course of action would be right or wrong in a given circumstance. This implies the reality and the need for God, the Revealer of truth. In no other way could anybody know anything for certain, except to receive more knowledge from the one Being who knows all things and who cannot lie. All knowledge is centered in and attached to the Conscience, and grows from that seed. Otherwise all men were ignorant.
A person who acts according to Conscience can improve his discernment of right from wrong over time. A person who violates Conscience destroys it, and loses his insight on this matter with time and wrongful action. Right and wrong are absolute, meaning they do not change from person to person or with time. What changes over time is the degree to which a person is aware of right and wrong, or the degree to which we give heed to the moral compass. This is why some people today have moral insight that others do not.
"Normative" is a meaningless term except that it implies a rule. Indeed, rules are arbitrary in general. Whatever God says is right. By this means we can learn more about what is right that we didn't already know. Moreover, it comes with a self-proving mechanism: It will be consistent with what we already knew.
In summary, there are two prerequisites to having a complete map of morality: One is to have and use the moral compass (which we all have from birth), and Two is to have and use a means of obtaining additional knowledge of truth, that is, by study and revelation.
There's a question of how to interpret the question.
I interpret this question as being about the linguistic distinction between moral norms (thou shalt not kill) and norms that have little to do with morality (mow your lawn biweekly).
I interpret it as not being about the distinction between moral norms, and norms that are called moral but really aren't. That's the bigger question of "what is really moral?" which I'll decline to address here.
Moral norms are those that have to do with harming people (or sometimes animals/other non-human beings) or helping them. Is it right to execute a murderer? Do I have an obligation to save a drowning puppy? Those are moral issues. Sometimes moral norms extend to causing harm or benefit in a sense disconnected from people; for example, it may be considered immoral to deface the Mona Lisa, independently of any distress the action might cause people. Harm or benefit is the focus of moral norms.
Other norms are simply social customs - tradition, protocol. How shall I paint my house? How should I address a judge? What clothes should I wear to the party? These norms often have to do with displaying one's social status or in-group membership, or respecting the social status of others. They are arbitrary in the sense that they vary between different societies and could be changed, if people agreed, without causing much harm. If everyone agreed that instead of suits, men should wear togas to formal events, society would carry on generally unchanged, without substantially harming anybody. This is why the wearing of suits is a norm, but not a moral norm.
Arbitrary normative statements are just, well, arbitrary. Not eating pig is clearly not arbitrary. The rule stems from a well defined moral system of rules. The pig lives in terrible conditions and that is the ground for the rule. It belongs to a more comprehensive moral rule system that bases it's rules on the sufferings of animals. Is not putting on lipstick that in its development stage involved in systematic animal torture an arbitrary rule? Certainly not.
A normative rule is arbitrary if the rule is about arbitrary statements. Not flying when the Sun ecclipses on a moonday at 12 while eating pork of a questionable origin would be a rather arbitrary normative statement. It is the question if these statements exist in real life. There are always well defined grounds (moral laws) at their base.
If not eating pork is considered part òf a religeous system (as seems to be the case here) then the rule (statement( seems rather arbitrary. But who knows how this was once. It maybe continued its life as part of a complete system. But in general such rules (which might be different for different people) are part of a system that is rationally defined. There exìst different kinds of ratios. What is rational for one can be madness for others. The one man's good or right is the other woman's bad or wrong.