“Four corners of an instrument” is the principle that a document’s meaning should be derived from the document itself, i.e., from its language and all matters encompassed in it. According to this principle, information which does not appear in the document (extrinsic evidence) – such as the circumstances surrounding the document or the history of the parties signing it – must not be analyzed or relied upon to ascertain the document’s meaning.
[Last updated in September of 2021 by the Wex Definitions Team]