The use of three lines to denote the number 3 occurred in many writing systems, including some (like Roman and Chinese numerals) that are still in use. That was also the original representation of 3 in the Brahmic (Indian) … See more

According to Pythagoras and the Pythagorean school, the number 3, which they called triad, is the only number to equal the sum of all the terms below it, and the only number whose sum with those below equa… See more

• Three is the atomic number of lithium.
• Three is the number of dimensions that humans can perceive. Humans perceive the universe to have three spatial dimensions, but some theories, such as string theory, suggest the… See more

• The triangle, a polygon with three edges and three vertices, is the most stable physical shape. For this reason it is widely utilized in construction, engineering and design.
• In European alchemy, the three primes (Latin: … See more

• Philosophers such as Aquinas, Kant, Hegel, C. S. Peirce, and Karl Popper have made threefold divisions, or trichotomies, which have been important in their work.
• Hegel's dialectic of Thesis + Antithesis = Synthesis creates thr… See more