Let me note first that musicians most often write for four parts, which, they find, contain the full perfection of harmony. Therefore they call these parts elemental after the four elements. As every physical body is composed of the elements, so every perfect composition is composed of the elemental parts. The lowest voice part is called the bass; it is analogous to the element of earth, which I slowest of the elements. The next part in ascending order is the tenor, which is analogous to water. It is just above the earth and united to it; similarly the tenor immediately follows the bass, and its low tones are indistinguishable from the high tones of the bass. The next voice part above the tenor is called by some the contratenor, by others the contralto or alto. Its position, third and central among the voices, is analogous to that of air; as air blends in a certain way with water and fire, so the low alto tones blend with the high tenor tones, while the high alto tones blend with the low tones of the fourth and highest voice, the canto. This voice, called by some the soprano because of its supreme position, is analogous to fire, which follows air and holds the highest place.
—Gioseffo Zarlino, The Art of Counterpoint: Part Three of Le Istitutioni harmoniche, 1558