 A proper suppositio, in turn, can be either formal or material accordingly when it refers to its usual non-linguistic referent (as in "Charles is a man"), or to itself as a linguistic entity (as in ""Charles" has seven letters").Such a classification scheme is the precursor of modern distinctions between use and mention, and between language and metalanguage.There is a tradition called speculative grammar which existed from the 11th to the 13th century.