Maybe I don't get you right, maybe you're wrong. I'm not sure. The way I get it, you say "but" is just like "and". How's that possible? I could say: "you have got brown hair AND I have got black hair" (this indicates both of them are true). I could say: "you have got brown hair OR I have got black hair" (one of them would be true, but it is not specified which one [update
that would be XOR. At least one of them is true, in a programmer's view]). I could also say: (oh, I think I do understand you now) "you have got brown hare BUT I have got black hair" (again, both would be true). Ok.
Hmm, nice stuff to think about :)