Euclid’s first common notion is this: Things which are equal to the same thing are equal to each other.
That’s a rule of mathematical reasoning. It’s true because it works—has done, and always will do. In his book, Euclid says this is “self-evident.” You see, there it is, even in that two-thousand-year-old book of mechanical law, it is a self-evident truth that things which are equal to the same thing are equal to each other.
We begin with equality. That’s the origin, isn’t it—that balance? That’s fairness. That’s justice.