Deep and first. NOR-completeness (one gate builds everything), the logic of relations, and quantifier notation are rigorous, foundational, and genuinely his — arrived at independently and often earlier than the names that got the glory.
He buried his own light. Peirce published little, in scattered and difficult venues; much stayed in unread manuscripts. Frege, Russell, and Sheffer were credited for things he had already done — a loss of priority that was largely self-inflicted.
A whole cosmos beyond logic. Pragmatism, semiotics (the theory of signs), metaphysics, geodesy — a system of staggering scope, much of it unfinished and contested. He died poor and obscure; the rediscovery came decades later.
De Morgan's sphere showed NAND is universal; Peirce got there first, and from the other side. His arrow ↓ — "neither A nor B," what we call NOR — is, on its own, enough to express every logical function. Toggle A and B; the NOR result drives three gates built from nothing but NOR, and each reproduces its standard truth table. One sign, and all of logic follows.
Term logic could not say "every head of a horse is a head of an animal" — it needed relations and quantifiers. Frege built that in 1879; Peirce, independently, built it in 1883–85, and gave it the notation that stuck: Σ for "there exists" (a logical sum) and Π for "for all" (a logical product). And he saw the subtlety the whole subject turns on: order matters. Click the matrix to set who relates to whom, and watch two quantified statements diverge.
"The one [logical] science to which all the others minister … is the science of drawing necessary conclusions." — C. S. Peirce
A single connective (NOR, his ↓) suffices for all logic — 1880, predating Sheffer's stroke by 33 years. The deep reason one gate can build a computer.
Predicate logic with Σ/Π, independent of Frege; the logic of relations as a first-class subject — the spine of modern mathematics, databases, and program logic.
Gate kept on. The honest frame is priority and neglect. Peirce's results are real and often earliest — but he is not the sole author of modern logic: Boole, De Morgan, Frege, and Schröder are woven through the same story, and Frege's system was more complete and rigorous as a foundation. Peirce's genius was matched by a gift for obscuring it — unfinished manuscripts, hostile relations with academic gatekeepers, a chaotic personal life that cost him his one professorship (Johns Hopkins) and left him, after 1891, in deepening poverty. He spent his last years in rural Pennsylvania, often cold and hungry, writing thousands of pages almost no one read, kept alive by quiet help from his friend William James. The arrow that builds every gate, and the Σ and Π in every logic textbook, are his — recognised, in full, only long after he was gone. ⚑ He belongs beside [[george-boole]] and [[gottlob-frege]] in the spine; the lineage simply met him late, as the world did.