Conventionally, the third is third in importance to the root and fifth, with the third in all primary triads (I, IV, V and i, iv, v) being either major or minor. In jazz chords and theory, the third is required due to it determining chord quality.
^Kostka, Stefan; Payne, Dorothy; Almén, Byron (2013). Tonal Harmony with an Introduction to Twentieth-century Music (3rd ed.). New York: McGraw-Hill. p. 494. ISBN0-07-035874-5.