There is an obvious distinction between the _essence_ of a thing and the _ends_ or purposes for which the thing exists. For example, in a business partnership the _essence_ of the partnership is a legal instrument, whereas the _purposes_ or _ends_ of the partnership are various commercial projects. The following is a clear statement, by Father Vincent McNabb, O.P., [124] of Catholic teaching concerning the nature and end of marriage: "Marriage is an indissoluble state of life wherein a man and a woman agree to give each other power over their bodies for the begetting, birth, and upbringing of offspring. The natural and primary end of marriage is this duty towards offspring. But, as sin has despoiled the human will and disturbed human relations, marriage has now the secondary end of allaying sexual lust. "But it is a principle of ethics that what is primary cannot be set aside as if it were secondary, nor can the secondary be sought as if it were primary. To invert the ethical order is to bring in that disorder which is called sin. If the human act brings in a slight disorder, it is venial sin; if the human act brings in a grievous disorder it is a grievous or mortal sin. "It is a grievous disorder, and, therefore, a grievous sin, to desire satisfaction in such sexual intercourse as could not result in the begetting of offspring. "As the wedded pair have given each other power over their bodies it would be a grave sin for one to refuse either altogether or for a considerable time the fulfilment of the marriage debt. But it is not a sin if by mutual agreement the wedded pair refrain from the marriage debt for a time, or for ever. As a rule, and speaking objectively, it would be heroic virtue for a wedded pair to abstain for a long time, and still more for ever, from the marriage debt. To counsel such a practice indiscriminately would be a sinful want of prudence, and, in a confessor, of professional knowledge. "It is quite clear that by mutual consent, even without any further motive, the wedded pair can abstain from marital intercourse. Still more may they abstain for a time or for ever, for a good motive, e.g. in order to have time for prayer, for good works, for bringing up such family as they already have to support." Section 3. ARTIFICIAL STERILITY WHOLLY CONDEMNED Artificial birth control is an offence against the law of God, and is therefore forbidden by the Catholic Church. Any Catholic who wilfully adopts this practice violates the law of God in a serious matter, and is therefore guilty of mortal sin, an outrageous and deliberate insult offered by a human creature to the Infinite Majesty.