What's This (Notation)

[snipe292]

Hi, I am wondering what the "1]" is supposed to mean:



It's from Chopin's Prelude No. 20.  I'm guessing it has to do with the fingering.

[pskim]

play with the thumb

[will]

Yes it is the fingering.
The five note chord with the 1] would require an almost impossible stretch of the fingers if you were to play each note with a single finger i.e. finger 1 on Db, 2 on Eb, 3 on G, 4 on C and 5 on Eb.
So you play the two lowest notes, both Db and Eb using the thumb.  To do this simply lay your thumb across to cover the two notes. Voila.

[snipe292]

Okay, thanks.  That's what I thought it was, just wanted to make sure.