Quantisation of electric charge is a basic (unexplained) law of nature;
interestingly, there is no analogous law on quantisation of mass 9 Superposition principle should not be regarded as ‘obvious’, or
equated with the law of addition of vectors It says two things:
force on one charge due to another charge is unaffected by the
presence of other charges, and there are no additional three-body,
four-body, etc