An ordinance of reason for the common good, promulgated by the one who has the care of a community. As an ordinance, law is distinguished from a mere counsel or a suggestion. It is an order or command that imposes obligation or moral necessity to be obeyed. It is the imposition of the superior's will on the will of those who belong to a society, and must be expressed in a mandatory form, no matter how courteously phrased. As an ordinance of reason, though directly imposed by the will of the one in authority, it is first formulated by his intellect as the planning faculty behind the will. Since its purpose is to direct rational beings to do something, it must be reasonable. To be reasonable, a law should be consistent, just, observable, enforceable, and useful. It is consistent when it is neither self-contradictory nor in contradiction with other laws. It is just when it respects higher laws and distributes burdens equitably. It is observable when it does not demand the impossible because it is cruel or too difficult. It is enforceable when not only the law-abiding but everyone can be expected to keep it because it is supported by appropriate sanctions. And it is useful when it serves a valid purpose without needless restriction of human liberty.
A law is for the common good, and in this differs from a command, order, precept, or injunction laid on an individual person. Laws, therefore, always look to the benefit of the community as a whole, not a private or personal good. When they are territorial, they bind all who stay in a certain region, but only when they are there. Laws are relatively permanent. They are always from public authority and last until repealed, and they may bind succeeding generations, whereas personal orders cease with the death or removal from office of the one who gave them.
To promulgate a law is to make it known to those whom it binds. The way it is promulgated depends on the nature of the law, the customs of the people, and on circumstances of time and place. It is properly promulgated if the people can come to know about the law without much difficulty.
A law must be authoritative, which means that it must come from a lawgiver or legislator who has rightful jurisdiction. The lawgiver may be a physical person, which is a single individual, or a moral person, which is a body or a board passing laws by joint action. (Etym. Latin legere, to read; eligere, to choose; ligare, to bind; lex, law.)