SATB Style
S.A.T.B Style Lecture Notes: In S.A.T.B ., you would have to double a note for most triad chords. The safest note to double is the root or tonic . Another safe note that can be doubled is the fifth . The above shows the Tonic note ( G ) doubled in G major triad . Image from: https://www.schoolofcomposition.com/beginners-guide-to-4-part-harmony/ In some cases doubling the third is acceptable, but in most cases, it wouldn't be ideal because it can sometimes overpower the harmony. In Dominant chords, do not double the third because it's a tendency note. In most cases, doubling a tendency note is unacceptable because it would feel the need to resolve. Open Position - When there are chord tones between the intervals. Closed Position - When there are no chord tones between the intervals. Image from: https://www.thejazzpianosite.com/jazz-piano-lessons/jazz-chord-voicings/open-voicings/ In S.A.T.B , it is not acceptable to have an octave or more apart between the three up