Formal Logic Cards

Description: "A diagram that shaped two thousand years of logic, from Aristotle through Boethius to the medieval schools. Bold letters in circles, crossing diagonals and the formula A ⟷ ¬O, E ⟷ ¬I underneath. Aristotle's square of opposition with the four categorical propositions A, E, I, O: all S are P, no S is P, some S is P, some S is not P. Contraries, subcontraries, subalterns and contradictories. For logic students, philosophy teachers, medievalists, mathematicians and fans of elegant diagrams. A refined gift for anyone who enjoys formal reasoning and classical scholarship.

Description: "The foundations of classical logic, from Aristotle to Leibniz, in three lines. Clean symbols and minimalist icons make this a smart design for anyone who values clear reasoning. The three classical laws of thought in formal notation: identity A ≡ A, non-contradiction ¬(A ∧ ¬A) and excluded middle A ∨ ¬A, each with a simple icon. Nothing can both be and not be. For logic and philosophy students, math and computer science majors, programmers who think in booleans and teachers of critical thinking. A sharp gift for rational minds.

Description: A dark background displays a table with two columns: 'Label' and 'Expression'. The expressions are mathematical logic notations, including quantifiers, implications, and symbols. Below the table, in large white font, is the statement "ie: God exists."

Description: "Aristotle's Prior Analytics in one picture. A gold point for Socrates sits inside the circle of humans, inside the circle of mortal beings: deduction made visible, with the predicate-logic version underneath. The most famous syllogism, Barbara: all humans are mortal, Socrates is human, therefore Socrates is mortal. Drawn as nested Euler circles with the formal proof ∀x (H(x) → M(x)), H(s) ⊢ M(s). For logic students, philosophy majors, law students, debaters, math teachers and anyone who loves a valid argument. A classic gift for teachers, graduates and Aristotle fans.

Description: "No consistent formal system rich enough for arithmetic can prove all truths. A solid structure of axioms with an empty slot at the top and a statement hovering above it makes one of the great results of logic tangible. Gödel's incompleteness theorem (1931): a pyramid of axioms with one gold block, G, floating out of reach. True but unprovable, with the self-referential formula G ↔ ¬Prov(⌜G⌝). For mathematicians, logicians, computer scientists, physics and philosophy students, and lovers of self-reference and paradox. A brilliant gift for anyone fascinated by the limits of proof.