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Binary, or the decomposition of meaning into is and not. Pretty much all meaning is constructed in binary opposition; there's a reason why digital arithmetic is binary. Examples include:
  • Light v. dark
  • Hot v. cold
  • Friend v. enemy
  • Better v. worse
  • Po-tay-toe v. po-tah-toe
The binary is formed by relating two unities. Relationships come in two forms: symmetric and asymmetric.
An image of two black dots
In a symmetric binary, the two halves are indistinguishable except for the fact of their distinction. Symmetric binaries are relatively uncommon (the only example I listed above of a symmetric binary is "po-tay-toe v. po-tah-toe"), because they only happen when the distinction being drawn is meaningless.
An image of a black dot and a red dot
In an asymmetric binary, one of the two is treated as special, or distinct among the two. In a binary relationship, either can be treated as distinct, the two merely being opposites of each other [1].
[1]Symmetric binaries can always be converted into asymmetric binaries simply by selecting one. If the two were truly symmetric, this selection is WLOG (without loss of generalization). This is also the principle embedded in the axiom of choice. Note that the axiom only applies to uncountably infinite sets; the whole of any finite portion of reality is always chooseable, which is to say that from a mathematical perspective it's given, and need not be assumed.