substituency
Substituency is a term used in linguistics to describe a property of certain groups of words within a sentence that behave as a unit, called a constituent. Substitutability by a single pro-form is a common way to test whether a sequence forms a constituent. If a sequence can be replaced by a single word or phrase without loss of grammaticality, it is often treated as a constituent.
In English, typical substitutes include pronouns, pro-forms like do so, and short phrases such as there or
Another example of substitution tests is VP: John wrote the report, and Mary did so as well.
A PP can also be substituted: The key to the cabinet is missing. The key to it
Substituency complements other syntactic tests (movement, coordination) and is central to theories of phrase structure and
Substituency is prized for its clarity in illustrating how sentences are built from smaller units and how