The more you concentrate on the difference between these words the more clearly does it appear that while pleasure is something that comes to you from outside, happiness is something that, though it may often be "roused to reciprocity" by pleasure, is intrinsically a mental, or even a moral state. You could also, I think, maintain without contradiction that there is an implication of lastingness about happiness, whereas the idea of pleasure suggests something not only more physical but much more transitory.
