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person1990s-present

John Horty

Disciplines:
logic
deontic logic
artificial intelligence
philosophy of action

Summary

American logician and philosopher who extended the stit theory of agency to deontic logic, developing a formal theory of obligation based on agency in branching time, and contributed to the logic of defaults and reasons.

Core Contribution

Deontic stit: obligation is analyzed in terms of what agents must see to it that they bring about; this grounds deontic logic in a theory of agency and responsibility. Default logic: developed a preferential default logic that avoids problems with Reiter's original system. Reasons as defaults: practical reasons function as default rules.

Key Spikes & Highlights

  • Agency and Deontic Logic is a landmark in deontic logic — grounding obligation in a rigorous theory of what agents bring about in branching time, connecting deontic logic to action theory.
  • The reasons-as-defaults framework bridges the gap between the logic of defeasible reasoning (AI) and the philosophical theory of practical reasons — showing they are formally the same structure.

Notable Works & Achievements

Agency and Deontic Logic

Reasons as Defaults

Historical Influences

Nuel Belnap Georg Henrik von Wright

Intellectual Lineage

Analytic Logic Deontic Logic

Contemporaries & Peers

Nuel Belnap Henry Prakken

Minds Influenced

No recorded minds influenced.

Intellectual Posterity

Deontic Stit LogicDefault Reasoning

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