Marriage is generally used as a term for a social institution. As such it may be defined as a relation of one or more men to one or more women which is recognized by custom or law and involves certain rights and duties both in the case of the parties entering the union and in the case of children born of it. These rights and duties vary among different peoples, and cannot therefore all be included in a general definition: but there must, of course, be something which they have in common. Marriage always implies the right of sexual intercourse: society holds such intercourse allowable in the case of husband and wife, and, generally speaking, even regards it as their duty to gratify in some measure the other partner's desire. But the right to sexual intercourse is not necessarily exclusive. It can hardly be said to be so, from the legal point of view, unless adultery is regarded as an offense which entitles the other partner to dissolve the marriage union, and this, as we know, is by no means always the case.