 The principles of the grammatical expression—what makes an expression grammatical—are the modes of signifying (modi significandi) of its constituent parts (Rosier-Catach 1995), which are the parts of speech (partes orationis), i.e., noun, verb, participle, pronoun, preposition, adverb, conjunction, and interjection. The modes of signifying are, in turn, the formal constituent features of these parts (QPm; QPm-1980: 138–139).