The Judeo-Christian bible opens with an enlightened symbolic description of duality;
In the Beginning, God created the Heavens and the Earth. The Earth was without form, and void; and darkness was on the surface of the deep. And the face of God moved upon the surface of the waters.
The heavens are the subjective reality (the kingdom of heaven is within you), and the Earth is the objective reality. The formless objective universe (the Earth) was void of interaction. The surface of interaction was only stillness. God’s face upon the waters’ surface allowed for self-reflection, and God’s motion upon the surface of the water created waves of interaction.
Duality is easily the most commonly understood and agreed upon metaphysical distinction, and is quite well represented with meaningful examples. Dualistic pairs match their two parts easily to one specific side of division or the other. Some pairs obviously complement each other, but there may be confusion as to which side each member belongs, be it the objective or subjective. Often, members of such pairs can be seen as properly belonging to one side or the other depending upon the particular perspective taken. What is more important is that the alignments can be seen at all. As Einstein said, “The most incomprehensible thing about the world is that it is so comprehensible”.
Wave/particle duality is quite telling. When experiments are performed on an electron, the test will detect either a particle or a wave, depending on what is being looked for. If a particle is being looked for, a particle is found. If a wave is being looked for, a wave is found. The electron, and every other entity, is both and neither a wave and a particle. When observed, the entity is either one or the other. When unobserved a particle is both and neither.
When an entity is divided into its subjective and objective components, each of the two parts may still be divided into further objective and subjective parts. As example, speech may be divided into objective words and subjective meaning of the words.