In common describes something that two people or things both have. It almost always appears in the phrase have something in common: We have a lot in common. The word common on its own usually means something else: “frequent, ordinary”, and about a person, in British English, “vulgar, lacking class”. That's why in can't be dropped here.
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have + a lot/much/nothing/something + in common (with + person); in common with + noun
- My new flatmate and I have a lot in common: we both love hiking and hate early mornings.
- The two job offers have one thing in common: both require moving to another city.
- In common with many students, I work part-time to pay my rent.
What changed
First versionMy sister and I have a lot common, so we never get bored together.
RevisionMy sister and I have a lot in common, so we never get bored together.
Common can mean shared, as in a common interest, so a lot common may look logical. But here the idea of sharing comes from the whole phrase in common, and in is required. Without it, the sentence falls apart.
When something is used together rather than just similar, the word is shared: a shared kitchen in a flat with several tenants. In common is about similarity: the same tastes, habits or features.
Your turn
Tom and I have nothing ___: he loves football, and I can't stand sport.
Show the answer
in common — Tom and the speaker have opposite interests, so they share nothing: nothing in common. Without in, the phrase doesn't work, and common on its own means “ordinary”.
Describe someone you became friends with. Name two things you have in common.
I became friends with Lena at university because we have a lot in common: we both play the guitar and love old films.
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