An assumption or supposition of law that something which is or may be false is true, or that a state of facts exists
which has never really taken place. A fiction is a rule of law which assumes as true, and will not allow to be disproved, something which is false, but not impossible. Best, Ev. 419.
These assumptions are of an innocent or even beneficial character, and are made for the advancement of the ends of justice. They secure this end chiefly by the extension of procedure from cases to which it is applicable to other eases to which it is not strictly applicable, the ground of inapplicability being some difference of an immaterial character. Brown.
Fictions are to be distinguished from presumptions of law. By the former, something known to be false or unreal is assumed as true; by the latter, an inference is set up, which may be and probably is true, but which, at any rate, the law will not permit to be controverted.
Mr. Best distinguishes legal fictions from presumptions juris et de jure, and divides them into three kinds, affirmative or positive fictions, negative fictions, and fictions by relation. Best, Pres. p. 27,