Do you have any ideas?
Do you have some ideas?
I read somewhere that we use 'any' in negative sentences so I assume I can't use it here?
Antonis M. we use 'any' in negative sentences Yes, but not only in negative sentences. Questions also take 'any', so you can use it here: Do you have any ideas?
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Antonis M.we use 'any' in negative sentences
Yes, but not only in negative sentences. Questions also take 'any', so you can use it here: Do you have any ideas?
Do you have some ideas? is also possible, but less used. This suggests that the speaker thinks the other person really has some ideas.
CJ