A legal fiction is a presumption of facts that is intended to facilitate an equitable resolution to a legal situation. Legal fictions are assumed for convenience or when a case could not be resolved without adopting such a fiction. They cannot be used to controvert the law or impede justice.
When a court adopts a legal fiction, it either makes an assumption based on available information in a case or it presumes a fact in order to facilitate the hearing of the case. Sometimes the assertion is actually not true, but it is assumed to be so for the purposes of the court. People have an opportunity to challenge the assumption if they believe that it would result in a miscarriage of justice.
There are a number of situations in which creating a legal fiction may be necessary to apply the law or to resolve a case. It is not uncommon to use a legal fiction to avoid cumbersome and circuitous handling of a case in court. If a fact can be presumed to be true for the purposes of the court, it can move the case along more efficiently to a swift and appropriate resolution.
One classic example is corporate personhood. Prior to the widespread development of corporations, if people had legal grievances with companies, they could sue the owners or partners directly. Once companies started incorporating, there was no person to sue, so the legal fiction of corporate personhood was created to provide plaintiffs with someone to bring suit against.
Another situation comes up in adoptions. When adoption paperwork is processed, the natural parents of the child become, for legal purposes, strangers, while the adoptive parents become the child's parents. This legal fiction does not erase the genetic connection between child and biological parents. It does facilitate the adoption process, providing the adoptive parents with rights and responsibilities related to the child.
The handling of wills and estates can also involve legal fictions. One situation which can cause problems with handling an estate is simultaneous death, in which couples die together in accidents or catastrophes. If the contents of the wills conflict with each other, a determination must be made to decide which one died first and which will takes precedence. Since it is not possible to literally find out which person died first, the court creates a legal fiction so that the estates can be distributed appropriately.