There are something I don't get about the degrees of freedom(dof). For massive dirac spinor, there are four complex components or 8 dofs. But for electron/position, there are only 4 dofs in total ( electron up &down, position up&down). Does it mean the equation of motion eliminate the other four dofs? I don't think so if KG equation doesn't eliminate any dof. Actually, if we write the EOM of massive dirac spinor in terms of left and right-handed weyl spinor, right-handed spinor can be expressed in terms of the derivative of left-handed one and vice versa. Does it mean the two helicity spinors weyl spinors are not independent? I hope not, since they represent distinct spins. Then it comes to majorana spinor. We all know they can be described by only left-hand or right-hand weyl spinor. Two complex components amount to 4 dofs. But obviously there are only two dofs (spin up and down).