Modal Logic

Q: What is a Claude Code skill and how does the Modal Logic skill fit in?

A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Modal Logic is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Content category. Learn more at https://claudskills.com/learn/what-is-skill-md/.

Category: Content · Sub-category: translation · Last updated: 2026-05-21

Extending propositional and predicate logic with modal operators -- necessity and possibility, and their relatives (obligation, knowledge, belief, time). Covers Kripke possible-worlds semantics, accessibility relations, the main modal systems (K, T, S4, S5), translation from natural language, and applications in epistemic, deontic, and temporal reasoning. Use when ordinary logic is insufficient to capture distinctions like "must" vs "might," "knows" vs "believes," "always" vs "sometimes.

About this skill (catalog notes)

Modal Logic includes explicit scope boundaries (an explicit 'when not to use' or 'out of scope' section). At roughly 1,717 words the SKILL.md is on the longer end of the catalog distribution.

Indexed lastmod: 2026-05-21
Catalog position: Content · translation
Indexed related skills: 10

How Modal Logic fits the catalog

Modal Logic sits in the Content category under the translation sub-topic in the ClaudSkills catalog. There are 10 related skills indexed alongside it; comparing a few before installing usually reveals which fits your workflow best.

These notes are auto-generated from features detected in the SKILL.md file and from this catalog's structure — they aren't part of the source repository.

From the source SKILL.md

Modal logic extends standard logic with operators for modes of truth -- most centrally necessity (□, "box") and possibility (◇, "diamond"). "It is possible that it will rain" is not the same claim as "it will rain," and ordinary propositional logic cannot distinguish them. Modal logic can. The framework also generalizes: the same machinery handles obligation and permission (deontic logic), knowledge and belief (epistemic logic), past and future (temporal logic), and provability (provability logic). The common semantic foundation is Saul Kripke's possible-worlds model. This skill covers the…

What this skill does

Modal Logic is a community-contributed Claude Code skill in the translation sub-category. It ships as a SKILL.md file that Claude Code auto-discovers under ~/.claude/skills/modal-logic/ and loads when your prompt matches the skill's trigger.

When to invoke it: Use when ordinary logic is insufficient to capture distinctions like "must" vs "might," "knows" vs "believes," "always" vs "sometimes.

Who uses this skill

The Modal Logic Claude Code skill is built for content creators, marketers, copywriters, SEO professionals, and editorial teams. It's part of ClaudSkills (also referred to as Claude Skills or Claude Code Skills) — the open community-curated registry of 116,000+ SKILL.md files for Anthropic's Claude Code agent and the wider Claude ecosystem (Claude API, Claude Agent SDK).

How to install

Free

Manual install (2 steps)

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

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

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

📱 Install from your phone or desktop Telegram

Open @claudskills_bot on Telegram, tap Open Desktop App, and the desktop app installs this skill for you. Or share the bot link with a colleague — they get the same one-tap install. Learn more →

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.

Pro

For the full experience including quality scoring and one-click install features for each skill — upgrade to Pro.

See pricing → Download desktop app

Frequently asked questions

How do I install the Modal Logic Claude Code skill?

Install via the ClaudSkills desktop app (one click) or copy SKILL.md from the source repository to ~/.claude/skills/modal-logic/SKILL.md and restart Claude Code. Both flows are detailed at claudskills.com/install/.

What does the Modal Logic skill do?

Is this skill free to install?

Yes. ClaudSkills is an open registry — every skill keeps its source repository's license, and manual install via copy is free. ClaudSkills Pro ($9/mo, $79/yr, or $149 one-time) adds one-click install via the desktop app and a multi-signal Quality Score.

When should I use the Modal Logic skill?

Use Modal Logic when your Claude Code task falls under the Content category — specifically in the translation area. Claude Code auto-discovers installed skills and invokes the right one based on the task description, so you can also ask Claude directly (e.g. "use Modal Logic" or describe the task and let Claude pick). Browse related skills at /category/content/.

What is a Claude Code skill and how does the Modal Logic skill fit in?

A Claude Code skill is a SKILL.md file that lives under ~/.claude/skills/<name>/ and tells the Claude Code CLI agent how to perform a specific task (instructions, prompts, allowed tools). Skills are auto-discovered at session start. Modal Logic is one of 67,000+ skills indexed in the open ClaudSkills catalog, classified under the Content category. Learn more at /learn/what-is-a-claude-skill/.

Cite this skill

If you reference this skill in a blog post, paper, or documentation, you can cite it as:

APA

ClaudSkills. (2026). Modal Logic [Claude Code skill]. ClaudSkills. https://claudskills.com/skills/modal-logic/

BibTeX

@misc{modal-logic-2026,
  author    = {ClaudSkills},
  title     = {Modal Logic [Claude Code skill]},
  year      = {2026},
  publisher = {ClaudSkills},
  url       = {https://claudskills.com/skills/modal-logic/}
}

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Badge

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