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

Numenius said that Pythagoras

Pythagoras

Pythagoras of Samos was an Ionian Greek philosopher, mathematician, and founder of the religious movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is known about him...

 gave the name of Monad

Monad (Greek philosophy)

Monad , according to the Pythagoreans, was a term for Divinity or the first being, or the totality of all beings, Monad being the source or the One meaning without division....

 to God, and the name of Dyad to matter. 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. Later Neoplatonic Philosophers and idealists

Idealism

In philosophy, idealism is the family of views which assert that reality, or reality as we can know it, is fundamentally mental, mentally constructed, or otherwise immaterial. Epistemologically, idealism manifests as a skepticism about the possibility of knowing any mind-independent thing...

 like Plotinus

Plotinus

Plotinus was a major philosopher of the ancient world. In his system of theory there are the three principles: the One, the Intellect, and the Soul. His teacher was Ammonius Saccas and he is of the Platonic tradition...

 treated the dyad as a second cause (demiurge

Demiurge

The demiurge is a concept from the Platonic, Neopythagorean, Middle Platonic, and Neoplatonic schools of philosophy for an artisan-like figure responsible for the fashioning and maintenance of the physical universe. The term was subsequently adopted by the Gnostics...

), which was the divine mind (nous

Nous

Nous , also called intellect or intelligence, is a philosophical term for the faculty of the human mind which is described in classical philosophy as necessary for understanding what is true or real, very close in meaning to intuition...

) that via a reflective nature (finiteness) causes matter to "appear" or become perceivable.

See also

• Monad (Greek philosophy)
  Monad (Greek philosophy)
  Monad , according to the Pythagoreans, was a term for Divinity or the first being, or the totality of all beings, Monad being the source or the One meaning without division....
  
  
• Triad (Greek philosophy)
• Tetrad (Greek philosophy)
• Pentad (Greek philosophy)
• Decad (Greek philosophy)