From First Principles Thinking
Runs a focused fishbone (Ishikawa) only — breadth-first cause-category map for a multi-causal effect. Invoke via /fishbone only.
How this skill is triggered — by the user, by Claude, or both
Slash command
/first-principles:fishboneThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
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You are running in focused-fishbone mode. Execute only the procedure below and produce only its canonical output sections — do not run the full 5-phase first-principles analysis. Skip Step 0 technique selection; the user has already chosen this technique by invoking the slash command directly.
Use a fishbone diagram when the problem has multiple interacting causes with no single traceable causal chain — you need breadth across the cause space, not depth into one chain.
Good fit: multiple plausible contributing factors exist across different areas; the problem recurs despite surface fixes and the cause is unclear; you need a structured way to ensure no category of cause is overlooked before narrowing focus.
Not a good fit: the problem has a single traceable causal chain and you need to drill to the root cause — that calls for a 5-Whys analysis instead, which is a depth-first root-cause drill down one causal chain rather than a breadth-first map across categories.
The category set is chosen once, before brainstorming begins. Two paths: use the domain-neutral default set, or select a named preset that matches your domain. The decision rule below maps domain signals to the recommended choice.
The domain-neutral default covers most situations cleanly. Use it when no preset row in the table below clearly matches your domain.
| Category | What it covers |
|---|---|
| People | Human contributors — skills, behaviours, training, workload, decision-making |
| Process | Methods, procedures, workflows, sequences of steps |
| Technology & Tools | Equipment, software, instruments, physical tools, infrastructure |
| Environment | Physical surroundings, conditions, constraints imposed by the setting |
| Information | Data quality, availability, communication, documentation, reporting |
| Resources | Materials, budget, time, capacity, supply inputs |
Use a named preset when your domain maps cleanly to an established category vocabulary. Each preset's category list is fixed — do not rename or merge categories mid-analysis.
6M (manufacturing / operations): Machine, Method, Material, Measurement, Man (People), Mother Nature (Environment). Use when analysing a production or operations process with physical machinery and materials at the centre.
8P (service / marketing): Product, Price, Place, Promotion, People, Process, Physical Evidence, Productivity. Use when the problem sits inside a service delivery or marketing context where the customer experience and offer design are the relevant axes.
4S (service delivery): Surroundings, Suppliers, Systems, Skills. Use when the problem is a service-delivery failure and a compact four-category lens is sufficient — typically a narrower operational scope than 8P.
| Domain signal | Recommended category set | Note |
|---|---|---|
| Physical production line, factory floor, ops process with equipment | 6M | Machine and Measurement categories capture equipment and process-quality causes that the default set folds into Technology & Tools and Process |
| Service business — customer offer, channel, pricing, marketing mix | 8P | Covers the full service-marketing mix; too broad for narrowly scoped delivery failures |
| Service delivery operation — narrow scope, no marketing mix needed | 4S | Compact; suited to front-line service failures where offer design is not in scope |
| Software, knowledge work, cross-functional teams, research | Default (six categories) | Domain-neutral labels avoid manufacturing jargon; Technology & Tools and Information handle the technical axes cleanly |
| Unclear domain, or no preset row fits cleanly | Default (six categories) | The default set is always a valid fallback — prefer it over forcing a preset that does not fit |
The default set is always a valid fallback when no preset row clearly matches your situation. Choosing a preset that does not fit the domain produces misleading category labels and blank branches.
Define the effect. Write one sentence naming the observable problem — the effect to be explained. State what is happening, not why. Do not name a suspected cause.
Choose categories. Pick the category set by domain signal: use 6M (Machine, Method, Material, Measurement, Man, Mother Nature) for a physical production line, factory floor, or ops process with equipment; use 8P (Product, Price, Place, Promotion, People, Process, Physical Evidence, Productivity) for a service business with a customer offer, channel, pricing, and marketing mix; use 4S (Surroundings, Suppliers, Systems, Skills) for a narrow-scope service-delivery operation with no marketing mix; use the default six-category set (People, Process, Technology and Tools, Environment, Information, Resources) for software, knowledge work, cross-functional teams, research domains, or when no preset fits cleanly. The default six-category set is always a valid fallback. Lock the set now. Do not add, rename, or remove categories once brainstorming begins.
Brainstorm causes. For each category, generate candidate causes that could plausibly contribute to the effect. Work one category at a time. Do not evaluate or discard causes during this step — record everything.
Identify sub-causes. For any cause that is itself explained by a deeper cause, add a sub-cause beneath it. Two levels of nesting are typically enough; go deeper only where the extra depth changes what action is possible.
Prioritise and verify. Review the completed map. Identify the branches most likely to be contributing based on available evidence. Mark unverified candidate causes explicitly. Select the highest-priority branches for evidence gathering or further depth analysis.
Effect: The weekly team status report is consistently delivered late.
The cause map surfaces six categories of contributor. Before this step, the problem looked like a single individual submitting late; the map reveals that the process and environment categories carry causes independent of any one person.
Blank-canvas paralysis. Staring at empty category branches with no starting prompt is the most common reason a fishbone session stalls. Start by asking for the most obvious cause in one category — even a wrong answer primes the group to respond with corrections and additions. The diagram is a brainstorm scaffold, not a test.
Treating the diagram as a verified conclusion. Every entry on a fishbone is a candidate cause — a hypothesis, not a finding. A branch that looks plausible is not evidence that the branch is real. Presenting the completed diagram as a diagnosis without subsequent evidence gathering is the single most consequential misuse of the tool. The diagram's job is to generate hypotheses; verification is a separate step.
Using a fishbone when Five Whys fits. If the problem has a single traceable causal chain and the goal is to find the root of that chain, a fishbone adds overhead without adding breadth. The multi-category structure is an advantage only when multiple independent cause types are plausibly in play. When you already know the cause type and need to drill deeper, reach for 5-Whys instead.
The candidate causes mapped here enter the 5-phase methodology at
Phase 2 (Challenge Assumptions). Each branch on the fishbone is an untested belief —
the fourth assumption class in Phase 2's four-type scheme — because the diagram is a
brainstorm of plausible contributors, not a set of verified facts. Add each candidate
cause as a row in the Classified Assumptions Table with type untested belief.
Do not route fishbone branches directly to Phase 3 (Establish Ground Truths). A branch is promoted to a ground truth only after evidence confirms it — that promotion happens inside Phase 2's challenge-and-verify operation, not by skipping it.
For branches that warrant deeper causal investigation, pair the fishbone with 5-Whys: the fishbone is the breadth-first cause map that identifies which branch to investigate; 5-Whys is the depth-first root-cause drill that traces that branch to its actionable source. The two tools are complementary — fishbone first to survey the cause space, then 5-Whys to drill the highest-priority branch.
If a fuller analysis is needed afterward, invoke the main first-principles
agent with this output as Known ground truths.
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npx claudepluginhub chrisdavidson/first-principles-skill --plugin first-principles