There is no difference in meaning — someone and somebody are interchangeable in almost every sentence, and both are singular. Someone is roughly twice as common in written English and reads as slightly more neutral ("Someone has taken my umbrella"), while somebody sounds a shade more conversational ("Somebody's at the door"). Pick whichever suits the rhythm of your sentence. The one place they are not quite equal is the idiom "he thinks he's somebody", where somebody is strongly preferred.
The core difference: register, not meaning
Unlike most confusable pairs, these two are not distinguished by sense at all. Any sentence that works with someone works with somebody, and vice versa. What separates them is frequency and feel. Someone dominates in books, journalism and formal writing. Somebody turns up more in speech, dialogue and informal prose, and it carries a faint extra warmth or emphasis.
Using each one
- Formal or neutral writing: If someone objects, we will revisit the proposal.
- Dialogue and casual prose: Somebody should have told me the meeting moved.
- Emphatic, almost dismissive: He thinks he's somebody. Here somebody works as a noun meaning "a person of importance". Someone is possible in that slot, but it is much less idiomatic and loses the punch.
The same split runs through the whole family: anyone/anybody, everyone/everybody, no one/nobody. The -one forms lean formal, the -body forms lean chatty.
The test you can run
Swap them. If the sentence still means precisely what it meant before — and it will, in almost every case — then the choice is purely stylistic, so default to someone in anything you would call writing, and to somebody when you are writing the way people talk. The one place the swap costs you something is the "important person" sense above; if you could replace the word with a big deal, reach for somebody.
Then do one more pass for consistency: mixing everyone and nobody in the same paragraph is fine, but flipping between someone and somebody in adjacent sentences about the same person reads as carelessness.
Where writers actually trip up
Both words are grammatically singular, so they take a singular verb: Someone is waiting outside, never are. But the pronoun that refers back to them is normally they, and this is standard, not sloppy: Someone left their coat. Insisting on his or her here is a style choice, not a grammar rule.
Watch the two-word spellings, which mean something else entirely. Some body is a physical body (some body of water); some one means "some particular one" (some one of these files is corrupted). And the possessive attaches to else, not the pronoun: someone else's problem, never someone's else problem.
Frequently Asked Questions
Is "someone" more formal than "somebody"?
Slightly, yes. Someone is the safer default in reports, essays and business writing, while somebody is perfectly acceptable but reads as more spoken. Neither is incorrect in either setting.
Is it "someone has" or "someone have"?
Someone has. Both someone and somebody are singular and always take a singular verb, even though we refer back to them with they: "Someone has left their bag on the platform."
Is "somebody" ever wrong?
Only in the sense of an important person, where the two are not interchangeable in reverse — "he's somebody now" cannot become "he's someone now" with the same force. Otherwise the choice is free.