Deductive Reasoning

Chinese source (authoritative): ../../skills/deductive-reasoning/SKILL.md

Deductive Reasoning

Description

Perform rigorous legal deductive reasoning based on formal logic. Use this skill when the user asks to “analyze case logic”, “verify legal reasoning”, “extract a syllogism”, “map the relationship between case facts and legal provisions”, or “assess the validity of a legal argument”. Provides a formal-logic framework for legal reasoning that turns unstructured legal norms and case facts into valid, testable, and reproducible deductive argument chains (P-F-C).

Instruction Steps

Step 1: Input

Read the case materials provided by the user and classify them into the following three initial states (if missing, temporarily record as empty):

1. Major premise (Provision, P): Legal rules, including written law (statutes, regulations, rules) as well as case law, social norms, etc.
2. Minor premise (Fact, f/F):
   • Natural minor premise (f): Natural events, acts, states, etc. (parties’ oral statements or factual narratives, e.g., “A asked B to transport goods”).
   • Legal minor premise (F): Events, acts, or states with legal significance (a lawyer’s or judge’s characterization of natural facts, e.g., “A and B formed a carriage contract relationship”).
3. Conclusion (hypothesis) (Conclusion, C): Partial or final conclusions drawn in judgment documents (e.g., guilty/not guilty, breach/no breach). Partial conclusions include intermediate conclusions or hypothesis conclusions awaiting verification, such as issues summarized by the judge, or preliminary inferences by parties or counsel.

Example: 【Major premise】: empty 【Minor premise – legal facts】: empty 【Minor premise – natural facts】: Company Jia entrusted transport of a shipment of goods to consignee Company Yi. Company Jia’s legal representative contacted by phone and entrusted a certain motor transport company with the carriage. The motor transport company did not conclude a written carriage contract with Company Jia. During transport, a traffic accident caused by the driver’s negligence damaged the goods. Company Yi therefore could not receive the goods on time and suffered loss. 【Conclusion (hypothesis)】 Against whom should Company Yi claim compensation? Company Yi believes it can claim against the transport company.

Step 2: Reasoning

Strictly perform the following Parts A and B, and cycle alternately until all logic is closed and no further supplementation is needed:

A. Complete the logical structure of each part

1. Major premise (P): Organize the logical structure; if there is no express provision, supply an implied major premise. Identify the type:
   • Categorical syllogism: Applicable to constitutive elements and conditions of establishment. Form: All acts satisfying feature $X$ have legal consequence $Y$.
   • Hypothetical syllogism: Applicable to “if … then …” rules.
     • Affirming the antecedent (modus ponens): $X \rightarrow Y$; the facts satisfy $X$, $\therefore Y$. (Most common)
     • Denying the consequent (modus tollens): $X \rightarrow Y$; $\neg Y$, $\therefore \neg X$. (Used for defenses and excluding legality)
2. Minor premise (f/F):
   1. Clarify the nature, sequence, causation, and subordination of events.
   2. Clarify the legal relationships among subjects; check whether a legal relationship exists between each pair of subjects.
   3. Exhaust each relationship; mark missing or ambiguous legal relationships.
3. Conclusion (C): Rank and filter multiple conclusions; identify and mark “intermediate conclusions”.

B. Link relationships and identify the middle term

Note: The middle term appears in both premises but not in the conclusion. It is the bridge connecting the syllogism, typically the “condition part” of a legal rule.

1. Fact subsumption (f-F): Link from the natural minor premise to the legal minor premise; extract and state the middle term (e.g., the mediating concept from “failure to pay the balance” to “fundamental breach”).
2. Finding the norm (F-P): Link from the legal minor premise to the relevant legal major premise; extract and state the middle term that triggers the provision.
3. Deriving the conclusion (P-F-C): From the legal major premise and legal minor premise, reason to the conclusion; write it in a complete standard syllogism format; verify that the middle term has been correctly derived.

Step 3: Output

Each time this skill is invoked, output two parts strictly in the following format:

1. Explainable reasoning chain

Use a clear P-F-C structure diagram or hierarchical list to show how the conclusion traces step by step, through intermediate conclusions, legal minor premises, and natural minor premises, back and links to the corresponding major premises. Clearly mark the middle term used at each step.

Example:

1. Fact subsumption

3. Reasoning chain C1: Yi recovers from Jia

C1‑1: Jia owes contractual duties to Yi P1: All parties to a contract → bound by the contract F1: Jia and Yi are parties to the contract C1‑1: Jia owes contractual duties to Yi

C1: Yi may recover from Jia P3‑1: Breach due to a third party → liability to the counterparty F21: Bing’s negligence caused Jia’s breach toward Yi C1: Yi may recover from Jia

C2′: Yi recovers from Bing

P1: All parties to a contract → bound by the contract F3 (missing): Yi and Bing are parties to the contract C2′: Yi may recover from Bing

C3: Jia recovers from Bing

C3‑1: Bing bears liability to Jia for compensation P2: Carrier causes cargo damage → carrier bears liability for compensation F21: Bing caused cargo damage C3‑1: Bing bears liability to Jia for compensation

C3: Jia may recover from Bing P3‑2: Disputes between a party and a third party → handled according to law or agreement F2: There is a carriage contract relationship between Jia and Bing C3: Jia may recover from Bing

2. Validity explanation report

Verify the form of the reasoning against the following standards and output a report:

• Validity conclusion: Clearly state which parts of the reasoning chain are “valid” and which are “invalid”.
• Fallacy explanation: If invalid, specifically identify which logical fallacy it is. When verifying validity, strictly check the following three common logical fallacies:

1. Affirming the Consequent: - Erroneous form: $P \rightarrow Q$, $Q$, $\therefore P$.
   • Explanation: Treating “the result occurred” as “this must have been the cause”.
2. Denying the Antecedent:
   • Erroneous form: $P \rightarrow Q$, $\neg P$, $\therefore \neg Q$.
   • Explanation: Treating “this cause is absent” as “the result will not occur”.
3. Fallacy of Four Terms:
   • Erroneous form: All $A$ are $B$. All $C$ are $D$. $\therefore$ All $A$ are $D$.
   • Explanation: The middle term does not truly connect, or the concept was switched (the middle term must be distributed at least once).

Example:

Skill Boundaries & Troubleshooting Guide (Troubleshooting & Constraints)

Validity judgment depends only on form, not on content. Even if the major or minor premise is factually false, so long as the logical form is correct, the reasoning must still be judged “valid”.