Word classes

The word classes — also called grammatical categories or, in older usage, parts of speech — are the sets into which all the words of a language are grouped according to how they behave. Knowing which class a word belongs to is the foundation of all grammatical description: it is what lets us say that, in o gato dorme (“the cat sleeps”), gato is a noun, o accompanies it, and dorme is the verb that organises the sentence.

The criteria that define them

A word is classified not by its meaning in isolation but by the way it functions. Modern grammar relies on three criteria, weighted differently:

• morphological — what inflections the word admits (gender, number, degree; person, tense, mood). Only verbs conjugate; only nouns and adjectives vary for gender.
• syntactic — what positions it occupies and what other words it combines with. The article precedes the noun; the adverb modifies a verb, an adjective or another adverb.
• semantic — what kind of meaning it conveys (entities, actions, qualities, relations). This is the most intuitive criterion, but also the least reliable, and so it is subordinated to the other two.

The word correr (“to run”) names an action and is a verb; corrida (“a run, race”) names that same action but behaves as a noun — it takes an article and a plural (as corridas). The meaning is close; the class differs because the behaviour differs.

The ten traditional classes

Portuguese school grammar, following Cunha and Cintra, recognises ten classes, divided between variable words (which inflect) and invariable ones (which do not):

Class	Type	Example
Noun (substantivo)	variable	casa, Lisboa, saudade
Adjective	variable	alto, português, feliz
Article	variable	o, a, um, uns
Numeral	variable	dois, terceiro, dobro
Pronoun	variable	eu, este, quem, lhe
Verb	variable	ser, fazer, partir
Adverb	invariable	bem, ali, talvez, não
Preposition	invariable	de, em, para, sob
Conjunction	invariable	e, mas, porque, se
Interjection	invariable	ai!, olá!, oxalá!

The first six inflect; the last four keep a fixed form. The noun, the adjective and the verb form the core of the sentence — they name, qualify and predicate — while the remaining classes serve mainly to link and to refer.

Open and closed classes

A more revealing division opposes open classes to closed ones. The open classes — nouns, adjectives, verbs and (in part) adverbs — freely admit new words: every technical or social innovation brings fresh nouns and verbs (telemóvel “mobile phone”, descarregar “to download”, bloguista “blogger”). The closed classes — articles, pronouns, prepositions, conjunctions — form stable, small inventories that take in virtually no new members. The former are therefore called lexical (or content) words, the latter grammatical (or function) words.

The Dicionário Terminológico’s arrangement

The traditional description is not the only one. The Dicionário Terminológico (2008), in force in Portuguese schools, reorganised the classes in line with contemporary linguistics. The two most visible changes: the article ceased to be an autonomous class and became a subtype of a new category, the determiner (determinante, which also gathers demonstratives, possessives and others); and the numeral was, for the most part, folded into a quantifier (quantificador). The determiner is further distinguished from the pronoun depending on whether the word accompanies a noun or replaces it.

The result is again an inventory of ten classes — noun, adjective, verb, adverb, determiner, quantifier, pronoun, preposition, conjunction and interjection — but one more coherent in functional terms. Tradition and the Dicionário Terminológico describe the same language; they differ in their arrangement, not in the facts.

One word, several classes

Classes are not inscribed in the word: they depend on use. A single form may migrate from one class to another without changing its shape — a phenomenon called conversion or improper derivation.

For this reason the question “which class does this word belong to?” is fully answerable only when the word stands in a sentence. It is the actual function, not the bare word, that fixes the class.