All human beings have an intuitive knowledge of the universal moral law.

When humans have disagreements with one another – which happens a lot – how do we resolve them?

Do we fight it out like animals? Well, sometimes, sure. But, usually, we avoid physical altercations by using our words. To put it another way, we quarrel with one another. Quarreling is a distinctly human activity. We all do it.

Children quarrel all the time. They say things like "that’s not fair" and "but mum, you promised!"

And it’s not just children – adults are just as prone to petty quibbling. They say things like "Hey, I was there first," or "I helped you out, so you owe me." And, of course, lovers are wont to make the accusation
you’re lying." So, just what does this love of quarreling say about us?

The key message here is: All human beings have an intuitive knowledge of the universal moral law.

What’s common to all these examples is that the offended party appeals to some kind of moral principle such as fairness or honesty. What’s more, they always expect their opponent to adhere to the same principles. 

In practice, that’s exactly what we find. Conflicting parties rarely disagree about the moral principles. When someone is caught having done something wrong – maybe they stole something or lied to their partner – they’re unlikely to argue that the victim’s moral standard is at fault, that actually stealing or lying are good things. No, instead they’re anxious to provide excuses as to why they should be exempted in this particular case. They might say, "I’m hard up for cash right now" or "Sorry, I had a lapse of judgment."

So, even when people break the standards of decent behavior, they still feel, on an intuitive level, that they’ve actually done something wrong.

This intuitive aspect of morality is key. We might provide perfunctory reasons for our actions, but ultimately, all of us – children and adults alike – feel intuitively when something is right or wrong, fair or unfair.

The author calls this the law of nature – a universal standard of good and decent behavior that’s felt by all human beings.

Of course, this moral law of nature differs from what we ordinarily understand as a law of nature. You can’t exactly break the law of gravitation, say, but you are free to break or ignore moral rules. Even so, we should still think of morality as a law because it’s by no means an arbitrary human invention – all humans at all times have felt the same moral impulses.