Q:

Divide a face following an existing edge (not part of the face)

This is a basic beginner question which should have already an answer, but I don't know what to search for.
I have a mesh with an edge connected to two vertices of a face, but not part of the face:

I would like to know how the face and the edge can be converted into two quads:

I know that deleting the face and creating two new ones is possible, but I'm interested in a method not requiring to delete anything.

A:

You can create an edge there by selecting the two vertices of this provisional edge, and pressing the shortcut key J.

This nice tool works well even for creating several continuous edges

