I thought a bit of clarity on duality might be helpful, so I revisited my copy of The Pythagorean Sourcebook and Library, compiled and translated by Guthrie, who clarifies the nature of duality in Pythagorean terms in his introduction.
“If one represents the principle of Unity from which all things arise, then Two, the Dyad, represents duality, the beginning of multiplicity, the beginning of strife, yet also the possibility of logos, the relation of one thing to another… With the Dyad arises the duality of subject and object, the knower and the known. With the advent of the Triad however, the gulf of dualism is bridged, for it is through the third term that a relation or harmonia (joining together) is obtained between the two extremes. While Two represents the first possibility of logos, the relationship between one thing and another, the Triad achieves that relation in actuality.”
Guthrie,Â 1988,Â The Pythagorean Sourcebook and Library, Phanes, 21-22.Â