To paraphrase, the Non-Aggression Principle (NAP) is usually stated as "do not initiate force or fraud", or "if it harms none, do what you will", or "treat others as you'd like to be treated", or "live and let live". In more detail, “Do not initiate force or fraud against anyone else’s person or property." In other words, except for self-defense, don’t harm others, don’t harm or steal their property, don’t break your word, don’t try to coerce anyone by threatening to do any of these things, and don’t delegate or encourage anyone to do any of these things.
The Equal Rights Principle (ERP) states that everyone has equal inherent rights, there should be no special privileged class, no "divine right of kings". This also implies that a group of people, no matter how many, can't have more rights than any individual. You cannot delegate a right to another individual or group if you do not have that right in the first place.
The Individual Sovereignty Principle (ISP) is that we, as individual sentient human beings with free will, each have the right to do anything we want as long as we do not violate NAP or ERP; and that we create organizations (including governments) and we grant specific, limited, enumerated privileges to them, not the other way around; they have no inherent rights of their own (this latter point is further discussed here). These 3 principles (ISP/NAP/ERP) form the tripod upon which any viable and just civilization must be founded, but for simplicity, we shall hereinafter refer to them collectively as NAP. Here is a simple animated illustration of these principles.
Liberty is the state of freedom achieved when everyone abides by NAP. It's a fundamental right of all individual persons, not something granted by a government or constitution. Liberty is inherently ours by birthright, regardless of whether one believes it comes from God, Nature, the Universe, or the simple fact that we're sentient beings with free will. Logic and necessity demand that we respect each other's rights, or else we revert to the law of the jungle. That is why NAP is the civilized version of:
When most people ask themselves what is "Natural Law", they think of the "law of the jungle", survival of the fittest, essentially total violence and chaos, kill or be killed. This is how it is for wild animals driven by instinct. But we are sentient beings, intelligent, self-aware, with free will and (for most of us) a conscience. If the term "Natural Law" is to have any meaning for us, then what is the natural law, what does Nature have to say, for such an exceptional self-directed being which can utilize not only instinct and intuition but also logical reason?
Obviously, since we're still animals and survival is non-trivial for many of us, we're still subject to the law of the jungle as a last resort. But humanity is smart enough to create and use tools to better interact with our world and exercise more control over our lives. We have developed technology to such an extent that we are capable of (and interested in) much more than mere survival. We have the ability to rationally decide how we want to interact with each other - either violently or peacefully; either fraudulently or honestly. We can come up with more than one solution to a problem, and often some solutions are much better than others. We can thus come up with our own laws to live by, above and beyond the law of the jungle. Indeed, it is the nature of sentient beings to survive and prosper by interacting intelligently with each other, rather than acting short-sightedly like mere animals - and obviously it works better too. This is because by applying rational thought, we can discover or develop opportunities for working together to accomplish more than we could individually. This makes it in our own best interest to deal with each other as equals. Thus, coming up with the most workable and efficient and mutually life-enhancing set of laws would be one way of following our Natural Law. And the better job we do at this, the better we're living up to our true nature and thus fulfilling Natural Law.
Any systems where some people have more rights than others (like dictatorships) are closer to the law of the jungle, in that someone has to obtain and maintain power by force or fraud and use that power to get a better deal than others. This may seem to work well for the bullies but not for the victims; thus only a few people are lifted above the conditions of savagery. Even those few on top are still living like savages, since they have to continually maintain their power by force or else lose it. Thus, this system is inefficient and ineffective.
A system where all people have equal rights, however, is much more civilized, efficient, and constructive, because it creates the least amount of destructive conflict. Competition can still thrive and continue improving the species but can't get too far out of hand, because the system is self-balancing as long as most people understand and remember the main principle involved (NAP). And because everyone has equal rights, it's easier for people to cooperate and collaborate with each other to produce mutually beneficial results. Thus, everyone's life can be improved, and to a greater degree, under this system. Then almost everyone, almost all the time, is lifted far above the mere concerns of survival and the law of the jungle, so this does a much better job of fulfilling our potential and our true nature and thus Natural Law.
The above argument is based mostly on our rational nature to show how it works in principle independently of any particular religious context. In other words, it works no matter what religion one believes in, or even whether one believes in any religion at all.
So, the natural state of things is for all of us to have equal rights and to refrain from violating each other's rights - in other words, to always follow the Non-Aggression Principle. Thus, in effect, for humanity, NAP is the essence of Natural Law.
The term "Common Law" has several meanings or derivations. In one sense, it means the informal body of law (in effect) consisting of customary behaviors and practices of civilizations over millenia. In America, that tends to mean English Common Law. In another sense, it means what are the most common or universal laws all over the world despite the different laws in different countries or the different laws and rules that different religions impose on their followers. This is why Common Law must be secular to be truly neutral, universal, and common.
These can all be considered imperfect examples of trying to figure out what are the minimum universal common principles that people must live by in order to have a functioning civilization, without the extra laws and customs that are specific to particular countries or religions or cultures. If you've read this entire web page so far, it should be quite obvious that the answer is NAP. Thus, throughout the rest of this web site, the phrase "Common Law" (or more specifically "Universal Common Law") will be considered to mean NAP. This is what Common Law should really mean, and the world would be much better off if was truly the common (and only) law of the whole world.
Much of the confusion and conflict between different rules of conduct and systems of laws and ethics arises from treating all rules as though of equal importance. We've discovered that it greatly simplifies this problem if we consider the principles above (ISP/ERP/NAP) to be MUSTs (or more accurately, MUST NOTs) and the other principles of various systems to be SHOULDs. This gives us the immutable Universal Common Law as the core that everyone MUST follow, and the then additional laws, rules, customs, etc. of various religions and cultures are then the individual group of SHOULDs for those contexts, which often conflict with others. There's no problem as long as everyone follows the MUSTs. The problems arise when people confuse their SHOULDs for MUSTs and therefore try to impose them upon others. This often causes them to violate the MUSTs. If everyone would understand this and conduct themselves accordingly, everything would be just fine.
The other remaining ethical problem plaguing the world is that many people tend to quit thinking in terms of abstract principles and prefer to be told what to do, so they pick someone they like and trust that person to be right. They may apply some ethical principles in making their decision at first, but then they get intellectually lazy and band together and start thinking that if their idol or guru is saying or doing something (especially if others in the group agree) then it's probably right. After a while, they become "loyal" to that person rather than to ethical principles. Since that person is a fallable human being, mistakes can be made. Even worse, this situation encourages power-mongers to take advantage of others in order to increase their power, so this situation is biased toward encouraging unethical behavior - the more a charismatic "leader" bosses his mindless group of sycophants around (or manipulates them in more subtle ways), the more likely he's leading them to violate the rights of others (and thus violate the MUSTs) in order to further his own goals. This may be the primary means of spreading moral corruption. So always be suspicious of governments and other political organizations and probably large longstanding organizations in general (some say including organized religion and corporations), especially if they appear to be powerful or influential. Always question these and the people that are "loyal" to them, especially the most fanatical. These people may have traded their minds and disciplined, rational, abstract thinking for the ego gratification of always feeling like they're doing the right thing without the work of having to actually think about it. "Loyalty" to a person or even a cause is usually a bad idea and eventually invites this kind of stagnation. Instead, always evaluate considered actions in terms of right and wrong, based on these ethical principles, starting of course with the MUSTs, and then your own personal SHOULDs but only if the MUSTs have not decided the issue. If the person or cause you want to follow is also being this ethical, then you'll continue working together. If they're not, and especially if they still refuse after you point this out to them, then you're better off (at least ethically) withdrawing your support. If you want to be "loyal" to anything, be loyal to these ethical principles, the MUSTs.