All sciences have for their starting-point certain elementary notions which are furnished them by the common experience of mankind. There would be no arithmetic if men had not, as their wants increased, begun by counting and calculating, and if they had not already had some ideas of numbers, unity, fractions, etc.; neither would there be any geometry if they had not also had ideas of the round, the square, the straight line. The same is true of morals. They presuppose a certain number of notions existing among all men, at least to some degree. Good and evil, duty and obligation, conscience, liberty and responsibility, virtue and vice, merit and demerit, sanction, punishment and reward, are notions which the philosopher has not invented, but which he has borrowed from common sense, to return them again cleared and deepened. Let us begin, then, by rapidly enumerating the elementary and common notions, the analysis and elucidation of which is the object of moral science, and explain the terms employed to express them. =1. Starting point of morals: common notions.=--All men distinguish the _good_ and the _bad_, _good_ actions and _bad_ actions. For instance, to love one's parents, respect other people's property, to keep one's word, etc., is right; to harm those who have done us no harm, to deceive and lie, to be ungrateful towards our benefactors, and unfaithful to our friends, etc., is wrong. To do right is _obligatory_ on every one--that is, it _should_ be done; wrong, on the contrary, _should_ be avoided. _Duty_ is that _law_ by which we are held to do the right and avoid the wrong. It is also called the _moral law_. This law, like all laws, _commands_, _forbids_, and _permits_. He who acts and is capable of doing the right and the wrong, and who consequently is held to obey the moral law, is called a moral agent. In order that an agent may be held to obey a law, he must _know it and understand it_. In morals, as in legislation, _no one is supposed to be ignorant of the law_. There is, then, in every man a certain knowledge of the law, that is to say, a natural discernment of the right and the wrong. This discernment is what is called conscience, or sometimes the _moral sense_. Conscience is an act of the mind, a _judgment_. But it is not only the mind that is made aware of the right and the wrong: it is the heart. Good and evil, done either by others or by ourselves, awaken in us emotions, affections of diverse nature. These emotions or affections are what collectively constitute the _moral sentiment_. It does not suffice that a man know and distinguish the good and the evil, and experience for the one and for the other different sentiments; it is also necessary, in order to be a _moral agent_, that he be capable of _choosing_ between them; he cannot be commanded to do what he cannot do, nor can he be forbidden to do what he cannot help doing. This power of choosing is called _liberty_, or _free will_.