1) I would have called you, but I didn't know your number.
2) I could have called you, but I didn't know your number.
Can I use 2 in place of 1? Do they mean same?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this community1) I would have called you, but I didn't know your number.
2) I could have called you, but I didn't know your number.
Can I use 2 in place of 1? Do they mean same?
Edit after reading OP's comment to this answer.
The two sentences in the question are saying different things. In the first case would is certain, but in the second case could remains a possibility. So the second sentence reads like an excuse.
Referring to the examination question asked in comment, you might think the same applies, but it is a different situation because passing the examination is something outside of your control (only studying and attending are), so using would in the first sentence is wrong. I suggest the valid sentence is
I could have passed the exam if I had studied hard.
The first case is assuring someone that, had you had their number, you would have called.
The second makes no such assertion, but points out that because you didn't have their number, it was impossible for you to call.
This is because would expresses (potentially subjective) certainty (when used in this sort of situation - there is some variation due to the history of the word), while could expresses possibility.