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. This variation can include person, number, or gender 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.
Phi-features are often thought of as the "silent" features that exist on lexical heads (or, according to some theories, 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.
Agreement on nouns
Chomsky first proposed that the N node in a clause carries with it all the features to include person, number and gender. In English, we rely on nouns to determine the phi-features of a word, but some other languages rely on inflections of the different parts of speech to determine person, number and gender of the nominal phrases to which they refer. Adjectives also carry phi-features in some languages, however, they tend to agree in number and gender but rarely for person. In English, number agreement is not expressed through agreement of verbal elements like they are in other languages (though present tense verbs do agree in number with third person subjects). This is partly because English is a language that requires subjects and the subjects in English overtly express number. Instead, English number is a phi-feature that is inflected on nouns when the nominal phrase is plural. The most common in English is -s inflected on nouns that are plural:<blockquote>- Ducks, fridges, baseballs, cups, books, mirrors, cars, buildings, clowns, bridges, creams....</blockquote>Some cases of plurality in English require inflection within the noun to express the phi-feature of plurality:<blockquote>- Men, women, mice, teeth....</blockquote>Neither verbs nor adjectives are used to agree with the number feature of the noun that they are agreeing with in English.
Some languages, however, like Salish Halkomelem, differ from English in their syntactic categorization of plural marking. Halkomelem allows for both marked and unmarked plural forms of its nouns. It also allows for the determiners to be marked or unmarked in their plurality. Plural nouns and determiners in Halkomelem can be freely combined as well, but it appears that if a determiner is plural in a phrase it is sufficient to pluralize the noun that it modifies:
{| class="wikitable"
|+Plurality in Salish Halkomelem
!
!noun
!determiner
!translation
|-
!unmarked
|swíyeqe
|te
|man (plural OR singular)
|-
!marked
|swí:wíqe
|ye
|men (plural only)
|}
Gender
English is a language that does not have nominal phrases that belong to a gender class where agreement of other elements in the phrase is required. Dutch is another language that only differentiates between neuter and the common gender. Many other languages of the world do have gender classes. German, for example, has three genders; feminine, masculine and neuter.
Agreement on verbs
When phi feature agreement occurs on a verb, it typically marks features relating to grammatical function (subject versus object), person, or gender. A key area of verbal agreement is attraction, in which case verbs are sensitive to the grammatical number of a noun phrase that is not the expected controller, but is close in vicinity. In other words, agreement is understood to be a relationship between a probing head and a target goal in the probe's c-command domain.
Person agreement
In English, agreement on a verb is triggered by the highest DP in subject position of a finite clause. Overt agreement is found only in the present tense, with a 3rd person singular subject, in which case the verb is suffixed with -s:
{| class="wikitable"
|+English walk
!
!singular
!plural
|-
!1st person
|I walk
|We walk
|-
!2nd person
|You walk
|You (all) walk
|-
!3rd person
|He/she/it walks
|They walk
|}
In a null-subject language such as Italian, however, pronominal subjects are not required (in fact, in many null-subject languages, producing overt subjects is a sign of non-nativity). These types of "unstressed" pronouns are called clitic pronouns. Therefore, Italian uses a different inflectional morphology on verbs that is based on the person features of the nominal subject it agrees with:
{| class="wikitable"
|+Italian camminare ('to walk')
!
!singular
!plural
|-
!1st person
|cammino (I walk)
|camminiamo (we walk)
|-
!2nd person
|cammini (you walk)
|camminate (you all walk)
|-
!3rd person
|cammina (he/she walks)
|camminano (they walk)
|}
Tense
Past tense, present continuous tense and the future tense are the three divisions of time expression of the action of a verb. In languages such as English, verbs agree with their subjects and not their objects. However, in Mohawk, an Indigenous language of North America, verbs agree with their subjects as well as their objects. Interestingly in Mohawk, a predicate can be counted as a verb, like 'big'. As shown in 1a), the form of 'big' changes to express the particular grammatical function, tense.
<section begin="list-of-glossing-abbreviations" /><div style="display:none;">
CIS:cislocative
NE:Mohawk prenominal particle
</div><section end="list-of-glossing-abbreviations" />
This change utilizes /v-hne/ as can be compared with the verb present in sentence 1b), 'fallen'.
