Sister Sledge - We Are Family - YouTube
I've searched on YouTube a song named 'We are Family'
Why use the sentence without an article 'a' or 'the'?
Family as used in the title is an uncountable noun.
We don't use articles (a/the) to introduce such nouns.
Family can be countable or uncountable.
We need to be careful when thinking about the grammar of special text genre types such as titles, headlines, lyrics, elements of poetry, etc. The rules that describe more conventional prose are often deliberately abandoned or played with to attempt to achieve special meanings, double or blended meanings, etc.
We are a family can mean essentially the same thing as We are family or something very similar. If there is a difference intended in the title (and as the utterance is repeated in the lyrics of the song), it is likely that family is referred to in a more generalized sense, perhaps something closer to "We epitomize family" rather than simply "We are a particular family (among many other families)."
In this case, however, I don't see any reason to think about We are family differently in the song's title and lyrics differently than it is used in other genres (we might say ordinary prose, if there's such a thing).
The Oxford Advanced Dictionary marks [Personal pronoun] [be] family as informal in its definition of family as a noun that is "singular, uncountable":
2. [singular, uncountable] a group consisting of one or two parents, their children and close relations
- The whole family came to Grandpa's eightieth birthday party.
- The support of family and friends is vital.
- We've only told the immediate family (= the closest relations).
- I always think of you as one of the family.
- (informal) She's family (= she is a relation).
However, the expression seems to me not particularly informal in register. Perhaps it once was more so. Another dictionary does not mark it as informal:
In MacMillan Dictionary:
[UNCOUNTABLE] people who are related to you
We spent our vacation visiting family in Scotland.
We ought to help him, after all, he is family.
friends and family/family and friends:
We had Christmas lunch in the company of family and friends.
I would parse family in We are family as a predicate adjective, an adjectival subject complement, meaning "We belong to the same family" or "our relationship is that of family".
We can't ask her to leave. She's family.
That means "she is, or is like, a member of the [i.e. our] family".
In this phrase, "family" is being used as an an uncountable noun.
When used in this way, "family" has a more essential quality. It is as though "family" is a substance, and you're made of it.
Saying "we are a family" asserts that you're all related. You might say "my whole school is a family," which means that even without blood or marriage, you all consider yourself the same.
Saying "we are family" asserts your family bond, not the group. You might say "we are family" to explain why you were loyal to your siblings.
The singers in Sister Sledge are not just trying to tell you that they are related. They are talking about the active role they take in each other's life by being supportive and close to one another. So, they say "we are family."