Condition means in law a declaration or provision that upon the occurrence of an uncertain event an obligation shall come into force, or shall cease, or that the obligation shall not come into force until a certain event. Such conditions are known respectively as precedent or subsequent, resolutive, and suspensive. Physically impossible, and unlawful conditions in matters of contract annul the obligation to which they are annexed, but in questions under settlements and wills the opposite rule holds, and such conditions are ignored. Conditions in restraint of marriage are considered unlawful only where they are absolute and imposed on persons otherwise entitled to succeed. A potestative condition is the technical name for a condition in the power of one of the parties. It is an important doctrine of contract law that if a debtor does anything to prevent the accomplishment of a condition, he becomes liable as if the condition had occurred. Many most important conditions are merely implied—e.g. in a marine policy that the ship is seaworthy. In bankruptcy, dividends are set aside to meet conditional obligations. Again, in sales on credit, solvency is an implied condition, and where the buyer is declared insolvent, the seller may refuse to proceed. A good instance of a suspensive condition is that of sale on approbation, or on sale and return. The doctrine of condition in feudal grants is in the law of Scotland very simple. Apart from entails, which were authorised by statute, such conditions must be intended to protect some valuable interest of the superior. Such are the clauses of pre-emption, the now obsolete clause prohibiting subinfeudation, clauses to preserve the plan of a town, or to prevent nuisances. Probably a condition against public-houses is valid, as in the case of the Grangemouth feus by Lord Zetland. If properly inserted and recorded in the titles, such clauses may entitle the superior not merely to refuse an entry under the old law, but to reduce the vassal's title.
Conditions of sale is the name used in England for what are called articles of roup in Scotland. These are generally printed along with the particulars of sale and distributed among those attending the auction. They provide what sort of title the purchaser is to accept. Similarly, conditions are prefixed to catalogues of furniture and books.