What's the simplest, most direct way to derive the lagrangian of the SM? I saw earlier today: L[S M] = L[Dirac] + L[mass] + L[Gauge] + L[Gauge/psi] That seems like a good starting point. I like it because it says the SM Lagrangian is simply the sum of four lagrangians. The next step seems to be that one needs to say what each of the four parts are. I am trying to get at this by using the absolute minimum amount tough mathematical concepts/language, at least to start with.