# Necessity Sufficiency

> Strategy: Probability of Necessity and Sufficiency (PNS/PS) — systematically evaluate whether each factor is necessary, sufficient, both, or neither for the conclusion.

- Skill: `yogsoth-ai/necessity-sufficiency` (Agent Skill)
- Install (CLI): `npx skillmds@latest add yogsoth-ai/necessity-sufficiency`
- Raw SKILL.md: https://api.skillmd.com/api/skills/yogsoth-ai/necessity-sufficiency/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: yogsoth-ai (https://skillmd.com/u/yogsoth-ai)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/yogsoth-ai/necessity-sufficiency

---


# Necessity-Sufficiency Strategy

PNS/PS framework: classify each factor by its causal role — necessary, sufficient, both, or neither.

## Method

1. **causal-claim-extraction** identifies all causal claims
2. **factor-enumeration** lists candidate causes
3. **necessity-evaluation** tests: would conclusion fail WITHOUT this factor? (PN)
4. **sufficiency-evaluation** tests: would this factor ALONE produce conclusion? (PS)
5. **single-factor-removal** provides evidence for necessity judgments
6. **load-bearing-identification** classifies factors into quadrants

## Classification Quadrants

- **Necessary + Sufficient**: Load-bearing walls (removal collapses conclusion)
- **Necessary + Not Sufficient**: Required but not enough alone
- **Not Necessary + Sufficient**: Redundant paths to conclusion
- **Neither**: Decorative factors (safe to vary)

## Budget Table

| Parameter | S | M | L |
|---|---|---|---|
| Factors tested | 5 | 10 | 20 |
| Necessity evaluations | 3 | 6 | 12 |
| Sufficiency evaluations | 3 | 6 | 12 |

## Orchestration

```
causal-claim-extraction → factor-enumeration
→ [for each factor]:
    necessity-evaluation (PN score)
    + sufficiency-evaluation (PS score)
    + single-factor-removal (supporting evidence)
→ load-bearing-identification (quadrant classification)
```

## Subagents

- causal-claim-extraction (claim identification)
- factor-enumeration (candidate listing)
- necessity-evaluation (PN scoring)
- sufficiency-evaluation (PS scoring)
- single-factor-removal (evidence generation)
- load-bearing-identification (classification)

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## Available Tactics

Optional, no fixed order; the final leaf is always a sop.

| Tactic | When to use |
| --- | --- |
| causal-necessity-testing | Tactic: Extract causal claims, evaluate probability of necessity (PN) and sufficiency (PS) for each, classify into necessity-sufficiency quadrants. |
| systematic-factor-ablation | Tactic: List all factors, remove one at a time, assess conclusion stability, rank factors by load-bearing importance. |

## Available SOPs

Optional, no fixed order; the final leaf is always a sop.

| SOP | When to use |
| --- | --- |
| causal-claim-extraction | Extract all causal claims (X causes Y, X leads to Y, X enables Y) from an artifact, producing a structured list of cause-effect pairs. |
| factor-enumeration | List all key factors, conditions, and assumptions that support or enable the artifact's conclusion. |
| load-bearing-identification | Identify which factors are "load-bearing walls" — factors whose removal would collapse the conclusion. |
| necessity-evaluation | Evaluate the probability of necessity (PN) for a causal factor — would the conclusion fail if this factor were absent? |
| single-factor-removal | Remove one specified factor from the artifact's support structure and reason about how the conclusion changes. |
| sufficiency-evaluation | Evaluate the probability of sufficiency (PS) for a causal factor — would this factor alone be enough to produce the conclusion? |

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