Thank you so much for clearing out my doubts. You truly are a genius! :-)
Two Different Parts written in on Staff by: David from www.piano-play-it.com
Hi Emma,
Excellent question you've got here!
Let's start with number once which is simple. In this case both the upper voice (e-d-d-c) and the lower one (c-b-b-a) should be played with the right hand. These are simply thirds (Follow the Musical Intervals piano lesson if you don't know what a thrid is) going down.
In number 2 you see a reduction. If you saw this on a choir sheet for example, then one group (The Alt for example) will sing the upper voice (e-d-d-c) and the Tenors will sing the lower part (c-b-b-a).
If you saw number 2 on a piano chart the right hand will probably play the upper part and the left hand will play the lower part. Since the voices are close to each other it was probably more comfortable to write them on the same staff, yet their stems are going to different direction to state the independence of each voice.
Now, in Bach chorals for example you'll see the number 2 since it is written for Choir. Each voice is independent and that's why you'll the stems going down for the lower voice to show that the lower part is sung by a different group (Sopraan, Alt, Tenor and Bass in a standard choir.)
Is this clear? Let me know if you didn't understand.