Ambiguity on the Factum Law and Legal Definition

Ambiguity on the factum is an ambiguity in relation to the foundation of an instrument. For example, questions such as: whether a testator meant a particular clause to be part of the instrument, or whether it was introduced with his knowledge, or, again, whether a codicil was meant to republish a former or a subsequent will, or whether the residuary clause, or any other passage, was accidentally omitted.

It is an ambiguity on the fact, not upon the construction which relates to questions such as: whether a particular clause shall have a particular effect.