Formal Logic

Quality score: 70/100 · Category: General · Sub-category: general-misc

Formal and informal logic for philosophical reasoning. Covers propositional logic (connectives, truth tables, tautologies), predicate logic (quantifiers, validity), syllogistic logic (Aristotle's original forms), natural deduction (introduction/elimination rules), modal logic (necessity, possibility, possible worlds), and a catalog of 15+ informal fallacies. Use when analyzing arguments, identifying logical form, evaluating validity and soundness, or detecting fallacious reasoning.

What this skill does

Formal Logic is a production-ready Claude Code skill (quality score 70/100) in the general-misc sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/formal-logic/ and loads when your prompt matches the skill's trigger.

When to invoke it: Use when analyzing arguments, identifying logical form, evaluating validity and soundness, or detecting fallacious reasoning.

Who uses this skill

The Formal Logic skill is built for Claude Code users and developers across all disciplines looking for general-purpose AI assistance. It is part of the open ClaudSkills registry, a community-curated catalog of 15,000+ capabilities you can install for Claude Code — the Claude CLI agent.

How to install

Free

Manual install (2 steps)

mkdir -p ~/.claude/skills/formal-logic
curl -L https://claudskills.com/skills/formal-logic/SKILL.md \
  -o ~/.claude/skills/formal-logic/SKILL.md

Or just download SKILL.md directly and drop it into ~/.claude/skills/formal-logic/. Claude Code auto-discovers it on next session.

Skills live at ~/.claude/skills/formal-logic/SKILL.md on macOS/Linux, or %USERPROFILE%\.claude\skills\formal-logic\SKILL.md on Windows. See the full install guide for step-by-step instructions.

Pro

One-click install via the desktop app

The ClaudSkills desktop app installs any skill directly into ~/.claude/skills/ with one click — no terminal required. Pro starts at $9/mo or $149 lifetime.

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Part of ClaudSkills — the open registry for Claude Code skills. · What's New · Install guide · About · llms.txt

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