What is the difference between reden, sprechen & sagen?

A few weeks ago a student asked me what the difference is between the verbs reden, sprechen and sagen.

If you look those words up in the dictionary you’ll find:

reden – to talk, to speak, to say sprechen – to talk, to speak, to say sagen – to say, to speak

Hmm, that’s useful, isn’t it?

Actually, if you think about it, when do you use talk, speak or say? Speak and talk are often interchangeable but speak is more formal than talk. A speaker is somebody who holds a speech whereas a talker pro...