My doubt is a vague one.Actually how is it possible that an operator in the time domain (say, d/dt) is a variable in Laplace domain ? (I am aware of the mathematical definitions) what is the "intuition" behind it? Coming to a simple control system an input x(t) is modelled as X(S) and output is modelled as Y(S) and the system i.e the transfer function is also modelled as say T(S) "which is a variable in s".As I previously mentioned a system is an function mapper but how is it a variable ? It is very perplexing