Phi features

In linguistics, especially within generative grammar, phi features (denoted with the Greek letter φ 'phi') are the morphological expression of a semantic process in which a word or morpheme varies with the form of another word or phrase in the same sentence.^[1] This variation can include person, number, gender, and case, as encoded in pronominal agreement with nouns and pronouns (the latter are said to consist only of phi-features, containing no lexical head). Several other features are included in the set of phi-features, such as the categorical features ±N (nominal) and ±V (verbal), which can be used to describe lexical categories and case features.^[2]

Phi-features are often thought of as the "silent" features that exist on lexical heads (or, according to some theories,^[3] within the syntactic structure) that are understood for number, gender, person or reflexivity. Due to their silent nature, phi-features are often only understood if someone is a native speaker of a language, or if the translation includes a gloss of all these features. Many languages exhibit a pro-drop phenomenon which means that they rely on other lexical categories to determine the phi-features of the lexical heads.