# Is potential difference or potential used in defining capacitance?

In my textbook I came across the capacitance of a certain body (i.e. a sphere, not two different spheres as in a spherical capacitor) and in it the formula,

$$Q = CV$$

where $V$ is the potential of the body with respect to the Earth. Now in a parallel plate capacitor, why do we choose the potential difference and not the potential of a single plate to the Earth?

• |It's just a matter of experimental observation that POTENTIAL DIFFERENCE for two conductors is found to be directly proportional to the charge. It is as similar as coeffcient of mutal in ductance. And by the way exact potential has no meaning. you are automatically taking potential difference by assuming nilpotent earth. – Prayas Agrawal Apr 4 '17 at 15:22