A detailed model adding dimensions of quantification and modality. Axis 1: Formal-Informal. Axis 2: Classical-Nonclassical. Axis 3: Deductive-Inductive. Axis 4: Monotonic-Nonmonotonic. Axis 5: Bivalent-Many-Valued. Axis 6: Truth-Preserving-Information-Preserving. Axis 7: First-Order-Higher-Order (quantification over individuals vs. over properties/functions). Axis 8: Extensional-Intensional (logic of truth values vs. logic of meanings/possibilities). These eight axes create 256 logical positions. Modal logic (necessity/possibility) is formal, nonclassical (in some classifications), deductive, monotonic, bivalent typically, truth-preserving, can be higher-order, intensional (deals with meanings across possible worlds). The 8 Axes demonstrate that the explosion of logical systems in the 20th century reflects different choices on these fundamental dimensions.
The 8 Axes of the Logic Spectrum "You think logic is just propositional calculus. The 8 Axes show that's one tiny point: formal, classical, deductive, monotonic, bivalent, truth-preserving, first-order, extensional. Modal logic changes intensional. Fuzzy logic changes many-valued. Nonmonotonic logic changes monotonic. The axes map the entire universe of logic—and you're still in the first galaxy."
by Dumu The Void February 25, 2026
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