Then it's not 'yes'
“” Yes, but ... “
Then it’s not ‘yes’ “
Nonsense, a yes, but. . . is still a yes, just with more to it.
For instance, if you rang the bell and I answered, and you asked, “Is your father home,” and I said, “Yes, but he is asleep,” - my yes is still a yes, I am just giving you additional and pertinent information.