When doubling certain notes in the right hand chord shapes sometimes there are double stems and sometimes there arent. Can someone please explain the rules? Here you can see the upbeat shows a double G using a double stem while the downbeat before shows no doubling at all. Does this mean the texture is reduced to 3 parts or does it mean that the G is doubled? I recall reading somewhere that if the alto and soprano are doubled no double stem is used but if the inner voices are doubled then you do use a double stem. I am not sure though so need clarification.
There seems to be an attempt to maintain 3-voice texture in the upper stave. (Whether there is any point in doing this in a keyboard part is another question. Maybe if it's a reduction of a choral score, used for rehearsal. Otherwise, why?)
But the attempt is abandoned on the second chord. If there's a 'rule', it's being broken!
Not all printed music is perfect.
Note that with a piano voices have a bit of a different meaning than in an ensemble piece. Thus in musical engraving of such music the choice of voices would be made so that the music is easy to understand and to read.
In the bottom example you will notice a bit of a hole in this one part. As everything else is pretty dense this is a bit distracting, thus the top example is easier to read.
Does this mean the texture is reduced to 3 parts or does it mean that the G is doubled?
I figure if someone splits stem directions, and the rhythm is the same for each "part", then the point is to indicate real parts. The OP's sample notation can't make up it's mind!
FWIW, it could have been notation with all shared stems, except for bar 2, beat 2, where there isn't uniform rhythm and you really must split stems...
...this kind if mixing of shared and split stem directions seems to be the usually keyboard notation. It means there is no intention to convey 3 or 4 part writing, and uses the split stems only when the rhythm requires it.
But, if we go with the idea that the original example is trying to show multiple parts with soprano stems up and alto & tenor stems down, then Musescore did it like this...
And if the doubled note were not the soprano/alto on
G4, but alto/tenor on
E4, Musescore did this...
Both make sense visually re. stems and note heads, but the first one would be better part writing, as the second one has parallel unisons.
I know I shouldn't use notation software as a notation best practice manual, but I don't have a copy of Behind Bars.
In the OP's example, I guess the editor forgot about the stem for the first eighths of down beat two, and wanted to avoid a double note head to indicate unison for the upbeat eighths.