I mean I know they are linear since they obey the ohms law. But I don't quite understand the reasoning that since, say, V=Ldi/dt and taking a derivative is a linear operation therefore it is a linear device?? I can verify that sin'(x) = cos(x) or sin(x+90) so the signal is time shifted but its form remains the same. That sounds logical to me but that has nothing to do with the fact that differentiation is a linear operation (which I believe is related to limits and differentials dy=m*dx etc). But what if we feed some sort of a high order polynomial instead of sin into L? Then taking derivative would distort the signal and would make the transformation nonlinear. So is it only linear when the signal is sin or cos?