Agreement of un, una, uns, unes

Use un with masculine singular nouns and una with feminine singular nouns: un carrer, una plaça. The plural forms are uns and unes. They commonly introduce some unspecified members of a set rather than a known group.

In a longer noun phrase, keep agreement through the whole group: una idea interessant, unes idees interessants. A singular article does not become plural simply because the noun is followed by another noun: una capsa de llibres is one box of books.

An indefinite article can introduce a new referent that later takes a definite article: he comprat un llibre; el llibre és molt curt. Bare mass nouns and bare plurals are also possible, so English some does not always require uns or unes. Un can emphasize one item, while uns can also signal an approximate number, as in uns deu minuts.