The Encyclopedia Britannica defines legal fictions as follows:
legal fiction, a rule assuming as true something that is clearly false. A fiction is often used to get around the provisions of constitutions and legal codes that legislators are hesitant to change or to encumber with specific limitations. Thus, when a legislature has no legal power to sit beyond a certain midnight but has five hours more of work still to do, it is easier to turn back the official clock from time to time than it is to change the law or constitution.
The most common legal fiction is a corporation. At law a coporation is a form of legal person able to own property, transact business, be a party in court actions and face criminal charges. It is a legal fiction as a corporation is not a living person. Corporations were deemed persons by courts so that creditors could obtain and collect judgments agains them.
Adoption is a legal fiction. When a person or a couple adopt a child that child becomes their child. The creation of the new child is a legal fiction. The adopted child is not their biological child. They have not conceived the child. I understand adoption was created in ancient Rome to solve the problem of a family needed a male heir but lacking a male heir.
The doctrine of survival or presumption of survivorship in a common disaster is a legal fiction. Most commonly it was applied in a situation when a married couple are killed and it was not possible to determine which one was the first in time to die. By survivorship it was deemed that the younger was the survivor. The principle can be of great importance in determining what happens to an estate. To clarify what is to happen many wills have a clause that provides directions if the testator, the maker of the will, and their spouse die in a common accident. Where the principle still exists, it can be rebutted by evidence that one of the deceased lived longer than the other deceased.
In another estate situation if a beneficiary renounces, gives up a bequest, a legal fiction takes place. The beneficiary is deemed to have predeceased the maker of the will.
A controversial legal fiction has been the principle of terra nullius which held there were no property rights in land prior to European colonization. The concept was used by European nations to justify their creation of empires outside Europe. In the Mabo case in Australia the concept was rejected by the courts.
More obscure and complex legal fictions existed in English law in the past as Courts sought to do justice. An example is recounted by Frederick Schauer from the University of Virginia Law School in his 2011 article, Legal Fictions Revisited, which can be found on the Social Science Research Network at http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1904555:
Thus we see the classic example of Mostyn v. Fabrigas, decided by the King’s Bench court in 1774.32 Fabrigas, a resident of the Mediterranean island of Minorca then occupied and controlled by England, was imprisoned by Mostyn at the time the governor of the island. Because no suit could be brought against Mostyn in Minorca without the approval of the governor, and because the governor was the defendant in the very lawsuit Fabrigas wished to pursue, Fabrigas sued instead in the Court of Common Pleas in London for trespass and false imprisonment, and proceeded to win a jury verdict of 3000 pounds. On appeal, Mostyn claimed, correctly, that the trial court had been granted jurisdiction only in cases brought by residents of London, but Lord Mansfield, recognizing that denying jurisdiction here would leave someone who was plainly wronged without a legal remedy, concluded that Minorca was part of London for purposes of this action. That conclusion was plainly false and equally plainly produced a just result, and thus Mostyn v. Fabrigas represents the paradigmatic example of using a fiction to achieve what might in earlier days have been done through the vehicle of equity.
I do not believe I have read a work of legal fiction featuring a legal fiction. It is easy to get lost in the abstract world of legal fictions. In the end legal fictions are just as untrue as legal fiction but their acceptance at law makes the unreal to be real.