The individual can form sums by selecting any combination of the four notes, including selecting no notes (which sums to 0). For each note, there are two possibilities: either it is included in the sum or it is not. With four notes, there are 2^4 = 16 possible combinations. However, one of these combinations represents selecting none of the notes, resulting in a sum of zero. If the question implies forming non-zero sums, then there are 16 - 1 = 15 distinct sums possible.