◄ UD0   ← Leibniz   LOGIKĒ · VII   ·   → the gate (PSĒPHOS)
LOGIKĒ · VII · the destination — logic becomes algebra

George Boole

1815 – 1864 · Lincoln, England · self-taught, professor at Cork · author of The Laws of Thought
Leibniz dreamed that logic could be an algebra. Boole, a shoemaker's son who taught himself mathematics, simply did it. He let 1 stand for true and 0 for false, and discovered that the laws of reasoning are the rules of an algebra: AND is multiplication, OR is addition, NOT is 1 minus. Reasoning, made calculable at last. He could not have known that seventy years on, an engineer named Shannon would notice that an electrical switch is also a 0 or a 1 — and that Boole's algebra was therefore the blueprint of every machine that would ever think.
✓ STRONG

Logic IS algebra. AND=×, OR=+, NOT=1−x, true=1, false=0, with the law x²=x — this is Boolean algebra, exact and foundational, and (via Shannon) the literal basis of every digital gate.

◐ REFINED LATER

His version was quirky. Boole used uninterpretable steps (x+x = 2x, even division). The clean modern algebra — where x+x = x — was tidied by Jevons, Peirce, Schröder after him.

◔ COMPLETED BY OTHERS

He laid the stone. It's propositional/class logic only (no relations → Frege); and the circuit link that made it the world's logic is Shannon's (1937), seventy years on.

I · The algebra of 0 and 1

Set x and y to 1 (true) or 0 (false) and watch each logical operation compute as ordinary arithmetic — and land on exactly the right truth value. This is the whole revelation: "x and y" is literally x times y; "not x" is literally 1 minus x. Reasoning carried out as a sum.

x =
1
y =
0
— click to flip
No new ideas were needed — just the audacity to treat true and false as numbers. Every gate symbol an engineer draws is one of these four arithmetic expressions, frozen into copper.

II · x² = x — the law that makes it logic

What separates Boole's algebra from ordinary algebra is a single strange equation: x² = x In normal numbers that holds for almost nothing. In logic it must hold for everything — and the only numbers that satisfy it are 0 and 1. That one law is the whole confinement: it forces every quantity to be true or false, nothing in between. Its twin, x(1−x) = 0, is Aristotle's old law of non-contradiction, now written as arithmetic.

y = x (straight) and y = x² (curve) meet only at 0 and 1 — the only solutions of x²=x
x · x = x  ⟹  x ∈ {0, 1}
x(1 − x) = 0  // non-contradiction
x + x = x  // (modern) OR is idempotent
"Nothing can be both itself and its opposite" — the firmest law Aristotle named — turns out to be just x(1−x)=0. Twenty-two centuries of logic, reduced to a quadratic.
"…the laws whose expression it is… are the laws of the human mind." — George Boole, The Laws of Thought (1854)

III · Boole → Shannon → the gate

The leap that made Boole the most consequential mathematician you've half-heard-of came in 1937, when Claude Shannon realised an electrical switch is a 0 or a 1: open or closed. Wire two switches in series and current flows only if both close — that's AND, that's x·y. Wire them in parallel and it flows if either closes — that's OR. Flip the switches and watch the lamp obey Boole's arithmetic. Every chip in PSĒPHOS is this, a few billion times.

A B
two switches + a lamp · series lights only if A AND B closed · parallel lights if A OR B · the lamp = the Boolean value

Gate kept on. Boole's own 1854 system was rougher than the clean thing taught today — he let expressions pass through meaningless intermediate values (2x, fractions) on the way to a sensible answer, and it was Jevons, Peirce and Schröder who filed it down to the idempotent lattice (x+x=x) we call Boolean algebra. His algebra is also propositional — it cannot say "every" or "some" or "taller than"; that needed Frege, next in this line. And Boole himself never touched a circuit: the marriage of his algebra to electricity is Shannon's, written when Boole had been dead seventy years. He died at forty-nine — pneumonia, after walking miles through rain to lecture, then being wrapped in wet sheets by a well-meaning remedy. Seen in his lifetime as an ingenious curiosity; revealed, a century later, as the man who wrote the grammar of the machine age.