On certain types of music you will see the notation "SATB", and unless you have been in a choir somewhere along the line, you might not understand what it means.It means "soprano, alto, tenor, bass", and so music that is written in this way was obviously written for voices, not for the piano or some other instrument. But most every hymn book is written SATB, so what is a piano player to do?
If he or she plays it as it is written, it sounds vacant, because 4 piano notes cannot adequately mimic 4 human voices. So a piano player needs to be able to "see through" the 4 parts and come up with the chord those 4 notes are spelling out. Once the chord is known, then the pianist can fill in with a much larger sound to accompany the singers, or if playing solo, improvise based on the chord structure of the song.
