The Dyad is a title used by the Pythagoreans for the number two, representing the principle of "twoness" or "otherness".

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Numenius of Apamea, a Neopythagorean philosopher in the latter 2nd century CE, said that Pythagoras gave the name of Monad to God, and the name of Dyad to matter.^{[1][need quotation to verify]} Aristotle equated matter as the formation of the elements (energies) into the material world as the static material was formed by the energies being acted upon by force or motion.^{[citation needed]} Later Neoplatonic Philosophers and idealists like Plotinus treated the dyad as a second cause (demiurge),^{[citation needed]} which was the divine mind (nous) that via a reflective nature^{[clarification needed]} (finiteness) causes matter to "appear" or become perceivable.

• Monad
• Tetrad