As the transfer of property from the dead to the living, inheritance depends upon two fundamental and rather self-evident conditions – the decease of a praepositus and the survival of an heir. Positive proof that these conditions have been fulfilled may, however, be lacking. It may be uncertain whether a person is dead or not, or whether one who is potentially an heir is alive or not, or, finally, whether an alleged heir was alive or not at the time of the praepositus' death. Such uncertainty arises in the three principal cases of (a) missing persons, whose death or survival cannot be established as a fact; (b) persons dying in circumstances where the precise time of death cannot be ascertained; and (c) children in the womb.

In these situations the interests of other parties require a resolution of the uncertainty and an answer to the question of whether a succession has opened, and if so in favour of whom. This involves the law in a twofold task. First, in the absence of factual evidence, the decision as to whether the basic conditions of inheritance have been fulfilled must rest upon the best evidence available – namely, that provided by legal presumptions. The relevant presumptions must therefore be determined and the scope of their application defined. Secondly, the final resolution of the uncertainty by such presumptions must often await a future date or event.