"I could have been a contender." "The film was quite good, but it could have been better." "Your son's exam results are not very good, he could do better."
Thanks. I meant in present tense, can we always replace 'can' with 'could'? For instance: it is the best deal you can ever get. Can we simply replace can with could here? ... deal you could ever get. Can we do this for all present tense sentences?