Frege had a profound influence on philosophers like Bertrand Russell, Rudolf Carnap and Ludwig Wittgenstein.
Having visual impressions is, of course, necessary for seeing things, but it is not sufficient. What must be added is not anything sensible. And it is precisely this that unlocks the outer world for us; for without this non-sensible something, each of us would remain locked up in his inner world.
Frege worked at the University of Jena, in Germany.