[projektfu]

The potential difference can be measured between any two points in a circuit, but EMF is the source of electrical energy such as a battery or generator that produces the potential difference that can be considered to "drive" the circuit.

As I understand it, an EMF has to come from nonelectrical energy, such as chemical, thermal, mechanical, or electromagnetic energy. So if you are drawing your circuit with a battery, you could call that EMF but if you are drawing it with a generic voltage source, you would not call that EMF per se.

[sacrosancty]

That 2nd distinction seems weirdly unreal. Is there an example of a real generic voltage source that only uses electrical energy and not those other types, or are you just referring to an idealization that you might use in a circuit diagram?

[projektfu]

Many voltage sources are themselves circuits and the EMF element would be hidden therein.

[sacrosancty]

Hmm. So is it that an EMF can't be carried along conductors like voltage can and is only the original source of the electrical energy with no circuitry?