Fundamental similarity between resistor, capacitor, and inductors?
They can all be treated as impedance in the complex space:
$$
Z_L = j \omega L  
$$
$$
Z_C = \frac{1}{j \omega C}
$$
$$
Z_R = R
$$
You can then treat them (the complex impedance or Z) like you do resistors. You can do this because the circuit elements are linear and the equations are linear for a given frequency. (The supplies can also be converted to the complex space and you can analyze an AC circuit like you would in DC).