When was this written? Also, it's not entirely untrue to say that we know what electromagnetic force does, but not what causes it. They say it's a 'fundamental force', which is basically way of saying we can't further reduce it to explain in terms of other stuff. We don't know what any of the fundamental forces (electromagnetism, gravity, and the strong and weak nuclear forces) really are - we can only describe their effects on the world with maths ('what they do')