Hello, if have a question concerning the difference between " interference" and "diffraction". Interference can be created, by superposition of countable many wavefields. So if I have a countable amount of wave sources, then the superposition can be called an interference. In contrary, for diffraction, I need infinitely many such sources. These are usually considered to be the famous secondary sources of huygens. I dont quite understand, why this should be the case. Why isnt it possible to create an interference by superposition of infinitely many sources? And why is it not possible to have diffraction with only countable many sources?