Fiction, in law, a supposition which is known not to be true, but which is assumed to be true in order that certain conclusions and inferences may be supported. Fictions have been made use of in all legal systems, but in none more abundantly than in that of England. The important courts of queen's bench and exchequer acquired their general jurisdiction by means of the fiction of supposing in the one case a trespass and in the other a debt to the crown, which the defendant was not suffered to dispute. The old action of ejectment and the existing action of trover furnish cases of fictions which seem to us at this day utterly absurd, the supposed lease, entry, and ouster in the one case, and the supposed finding of the goods in dispute in the other, having no bearing on the merits of the case; but they nevertheless have had their use in enabling the courts to give suitable remedy for a wrong which otherwise might have gone unredressed in some cases. With few exceptions, no fictions are now retained in the law except such as have a beneficial purpose; and these are mostly fictions of relation, as where the title of an administrator is supposed to have attached at the death of the deceased, in order to enable him to recover for any trespass or misuse of the property prior to his appointment; and that of a purchaser at a judicial sale is made to relate back to the time of sale, though the title is not to pass until after the expiration of a period allowed for redemption.

Several rules are laid down in respect to fictions: 1. The law never adopts them except from necessity and to avoid a wrong. 2. They must not be of a thing impossible. 3. They are never admitted where the truth will work as well. 4. They are not admissible in criminal trials. The fiction, for instance, that the title of a purchaser at a judicial sale shall relate back and cover the period allowed for redemption, though admissible for the purpose of giving a remedy against a wrongdoer, would not be admissible as against the party whose previous title was divested, if by law he was entitled to a beneficial use of the property until the time for redemption expired. Fictions might undoubtedly be all rendered unnecessary by statutory provisions, but not many are made use of in the law at this time which create any confusion, or the removal of which could be of any service beyond giving a little more directness to legal proceedings, or expressing the legal right in language more suited to the comprehension of laymen.