Tetractys
The Pythagorean Triangle
The Pythagorean oath is not sworn by the tetractys. Sextus Empiricus, around 200 CE, quotes it as sworn 'by the man' who bequeathed the tetractys, meaning Pythagoras, 'for him they deified'.
Sextus Empiricus, Against the Logicians 1.94–95 (R. G. Bury, Loeb, 1935)
Ten points in a triangle of four rows, one to four, the figure the Pythagoreans held sacred.
More context
The tetractys is ten points arranged in an equilateral triangle of four rows, the Pythagoreans' sacred figure, also called the Tetractys of the Decad. Its rows were read as the point, the line, the surface and the solid. Its ratios, 2:1, 3:2 and 4:3, give the octave, the fifth and the fourth, the concords of musical harmony. Summing to ten, it stood for the perfect number. Pythagoreans swore by Pythagoras as the one who had bequeathed the tetractys, which they called the fount of ever-enduring nature.
Light
Invites logical clarity, cosmic harmony, and an appreciation for the elegant, underlying order and mathematical beauty of the universe.
Shadow
A tendency to reduce complex, emotional human experiences into cold, abstract equations, losing empathy in the pursuit of logic.