Trying to figure out the keys of several piano pieces by Schumann that I am just looking at and I don't get it. For example the fugues opus 72 and the Night Visions opus 23. They seem to be in no key at all but are written with sharps and flats in the beginning. Can anyone explain?

Thanks
Stokes

The Op. 72 fugues seem pretty clear cut to me as far as keys. They're in d minor, d minor, f minor, F major.

Nachtstucke looks a little more vague, though it appears it centers more or less around C major (notice the cadences at the end of the phrases - though it seems to wander around key-wise, it seems to usually end on a V-I in the key of C). As such, it seems appropriate to me that there are no sharps/flats in the key signature. It looks highly chromatic, so its no wonder there are lots of accidentals peppered in there. Just because a piece has lots of accidentals doesn't mean it has no key.