# Why do the different lepton generations have different masses?

I've been reading Mark Srednicki's book on Quantum Field Theory, and toward the end (Chapter 88), he describes how the different generations of leptons acquire mass via Yukawa interactions. However, I'm trying to work out why exactly the different families of leptons (electrons, muons and tauons) have different masses to eachother.

Can anyone explain? Or is this somehow linked to the unanswered question of why any of the fermions have the particular masses that they do?

The fermion masses result from Yukawa interactions after EWSB: $$m_f = \frac1{\sqrt 2} y_f v$$ Thus the Yukawa couplings govern lepton and quark masses.