The law prohibits as incestuous (i.e. unchaste) sexual relations, and, a fortiori, marriage, between certain near relatives, but the definition of which relationships are incestuous and which are not is quite chaotic, and certainly does not correspond, as is so often supposed, to a policy of preventing in-breeding. In principle, the law adopts the Table of Prohibited Degrees drawn up by the Church of England in 1563 — although the Church itself has since abandoned this list. This table is based on the proposition that a man and wife are “one flesh“, and therefore excludes a man from marrying relatives of his wife; and it treats “step” relationships as full blood relationships. As it excludes several relationships where no question of a mixture of blood need arise the religious character of the prohibition is evident. (Nevertheless, it is applied to persons of other religious faiths.) To confuse the issue still further, recent legislation has modified the original list by permitting a man to marry various relatives of a deceased wife (and correspondingly for the woman), although a similar privilege is not allowed where the wife is not dead but divorced. By a decision of 1797, Jews may keep concubines.
The law prohibits polygamy; a purist might observe that it prohibits what it has already made impossible, since it rules that when a married person goes through a form of marriage with a third party, no valid marriage subsists. Since mediaeval jurists recognized a distinction between marriages which were illegal but valid, and those which were invalid, the point is not just a verbal one; as a result of this view the crime which a person so acting commits and is punished for, is not bigamy but profanation of the marriage service. Modern legislators, however, have forgotten this, inasmuch as they have extended the penalties for this offence to apply to a person who goes through a form of marriage in a registery-office, where there is no religious service to be profaned.
The concept of a marriage which is valid but not legal persists, however, in another sphere, for persons under the age of 21 (but over 16) are forbidden to marry without their parents’ consent. If, nevertheless, they do so by making a false statement as to their ages, the marriage is valid — although the man is liable to as much as seven years’ imprisonment. No person under sixteen may marry. The age-limit was raised (from 14 and 12) in 1929. Setting the age-limit above the age of biological maturity has the interesting result that if a boy makes a girl under sixteen pregnant, he cannot, with the best will in the world, legitimize the child. Nor can he be convicted for rape.
The law does not attempt to regulate the frequency of intercourse (but see below for unconsummated marriages) and repeats none of the canon laws governing the mechanics of the sexual act, except that concerning anal intercourse. Practices involving persisted physical cruelty would, of course, provide grounds for divorce — though the cruelty must be both Physical and Persistent.