In Chopin's 10/12, measure 57 there are the dotted half notes, Eb C Eb. Are these sounded toether? In the following measure (58)the Eb B natural Eb configuration, are these played together or is the B natural sounded immediately after the Eb's?

They're all sounded together. The C and B are with the Eb's (they're just considered to be in a separate voice.)

Why would these notes not all sound together since the Eb,C,Eb in measure 57 all come precisely on the second beat and the Eb,B,Eb in measure 58 come on the first beat.

What would be the rationale, theoretical or otherwise, for not playing them all together?

Regards,

I think Frycek's rationale would be that in ms. 58 the B-natural appears to the right of the E-flats. I agree with Kreisler's multiple voicing answer. If the notes were to be played not together, then I would expect something different in the notation - either a grace note, or some different rests to indicate how much of a delay is to be given before the second note is played.

I've been playing them together. I'm reworking the piece and I was just second guessing my ignorant self. Thanks!

This explanation is unusual because the confusion resulted, I think, from a misreading rather than a 'rationale' for ambiguity. (Like BruceD, I can't find one either.)

Kreisler's explanation was factually correct, as the notation is standard: horizontal offseting is often required when simultaneous notes are in different voices, are on different stems, and have different durations.

Now I'm confused. Frycek just said she/he was already playing it correctly. I was agreeing with Kreisler (and with what you just restated above) and then provided the rationale for why it wouldn't be played separately. That way Frycek would have another reason why the notation didn't indicate playing it separately - there are cases where different voices are not necessarily played simultaneously.

It looks like the confusion was mine, so I apologize for adding to it. (I didn't understand what it meant to 'agree' with Kreisler's answer ... when in truth no other other answer was possible.)