From Longman Dictionary of Contemporary Englishyes and noyes and no spokenCLEAR/EASY TO UNDERSTANDused to show that there is not one clear answer to a question ‘Were you surprised?’ ‘Well, yes and no. I knew they were planning something, but I wasn’t sure what.’ → yes
Examples from the Corpus
yes and no• Not words we use much in the Civil Service, yes and no, even in the most impersonal contexts.• "Were you surprised?" "Well, yes and no. I knew they were planning something, but I wasn't sure what."• A decision is more a matter of yes and no: is this thing worth doing or is it not worth doing?• There was no significant difference to the manner in which yes and no responses increased over memory set size. 