Although the Standard Model itself is a very complicated theory, the basic structure of the model is fairly straightforward. According to the model, all matter is divided into two categories, known as hadrons and the much smaller leptons. All of the fundamental forces act on hadrons, which include particles such as protons and neutrons. In contrast, the strong nuclear forces doesn't act on leptons, so only three fundamental forces act on leptons such as electrons, positrons, muons, tau particles and neutrinos.