I am reading texts on fundamental physics about diffraction and interference. When comes to diffraction, it takes a single slit as example and using Huygen's principle to explain how the wave transmitt and form the pattern. It sounds like that the pattern is due to interference. One textbook even said that "there is no fundamentaldistinction b/w interference and diffraction ..." It is really confues 1) if there is no difference, why using different terms? 2) whem comes to a pinhole, can I say the resulting airy discs are also come from interference? 3) in Bragg diffraction (2D case), it is all about interference b/w reflected waves, why still call it "diffraction"?