Draft

The practical idea is the concept of current. The whole discussion about the direction of current seems confused because a current can be created two ways: either +positive charges moving in one direction, or -negative charges moving in the other direction. The two clouds of charge move right past/through each other in the same small space. (This is really different from water current, where there is just one type of water molecule flowing in one direction.)

Of course, depending on the material (copper wire or saltwater, or something else), the current may be composed of just one type of charge, or both. However, event though there are these different situations, we would like to create a definition of current that works for every case.

So now you are observing some current flowing in some arbitrary material. What direction is it flowing? What you see is + charges going one way, and - charges going the other way. You are in charge (sorry for the pun) of assigning a single direction of flow for the current. You are not allowed to say “the current is flowing both ways”, you have to pick one. What direction do you pick?

A long time ago some early engineers had to make this choice. They chose the direction the positive charge moves. Seems reasonable. (At the time, they didn’t know about the existence of the electron or proton.) We still use that choice today, and that choice is called conventional current.