Sequential Thinking

Structured step-by-step reasoning with hypothesis generation, elimination, and revision capability.

When to Use

• Complex problem requiring multi-step reasoning
• Debugging where root cause isn't obvious
• When mk:fix invokes diagnosis (Phase 3)
• Architecture decisions with multiple trade-offs
• Any situation where "I think it's X" needs evidence before acting

Do NOT use for: trivial fixes (typo, lint), single-file changes with obvious cause.

Process

1. State the problem — what is observed vs expected
2. Generate hypotheses — from evidence, NOT guessing. Each hypothesis needs: what evidence would confirm it, what would refute it
3. Test hypotheses — use Grep/Read/Bash to find evidence for/against each
4. Eliminate — mark each CONFIRMED, REFUTED, or INCONCLUSIVE with evidence
5. Conclude — state root cause with confidence level + evidence chain
6. Scope the fix — what must change to address root cause (not symptoms)

Adjust dynamically: expand if more complex than expected, contract if simpler.

Output Format

Use references/hypothesis-testing.md template. Key sections:

## Sequential Analysis: [problem]

### Hypotheses

| #   | Hypothesis | Evidence for | Evidence against | Status |
| --- | ---------- | ------------ | ---------------- | ------ |

### Root Cause

Confirmed: [root cause]
Confidence: [high/medium/low]
Evidence: [what confirms this]

### Fix Scope

[what must change — files, functions, logic]

Revision & Branching

When new evidence invalidates a previous conclusion:

• Mark revision explicitly: [REVISION of Hypothesis N]: [correction + why]
• When 2+ approaches viable: branch, evaluate each, converge with decision

Load references/core-patterns.md for revision/branching patterns. For advanced techniques (spiral refinement, multi-branch convergence): references/advanced-techniques.md For uncertainty + revision cascades: references/advanced-strategies.md For concrete examples: references/examples-debug.md, examples-api.md, examples-architecture.md

Diagnostic Frameworks

Load when a specific methodology fits the investigation:

• references/five-whys-plus.md — enhanced 5-Whys with bias guards + stopping criteria. Use for post-mortems, recurring problems, human-error investigations.
• references/scientific-method.md — hypothesis → falsifiable prediction → experiment → revise. Use for A/B tests, performance investigations, production incidents.
• references/kepner-tregoe.md — SA/PA/DA/PPA + IS/IS-NOT matrix. Use for multi-system bugs, contested root causes, high-stakes decisions.

Scripts

Track and format thoughts deterministically:

• scripts/process-thought.js — validate, track history, branches, revisions. Max 20 thoughts. node scripts/process-thought.js --thought "..." --number N --total M --next true node scripts/process-thought.js --summary (context-efficient handoff to mk:fix)
• scripts/format-thought.js — format as box/simple/markdown/json node scripts/format-thought.js --thought "..." --number N --total M --format json

Gotchas

• Premature conclusion: confirming first hypothesis without testing alternatives → test at least 2 hypotheses before concluding
• Evidence-free hypotheses: "I think it's X" without evidence → every hypothesis needs at least one piece of evidence
• Revision avoidance: refusing to revise when new evidence contradicts → revise explicitly, don't force-fit

Full list: references/gotchas.md

Workflow Integration

Called by mk:fix during diagnosis (Step 2). Receives input from mk:investigate or direct observation. Output feeds into fix implementation.

mk:investigate → symptoms + traces → mk:sequential-thinking → root cause → mk:fix