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What is a fishbone diagram?

A technique for sorting the causes behind a result (an “effect”) into categories as you surface them. Because the finished shape resembles a fish skeleton, it’s also called a fishbone diagram (or Ishikawa diagram).

• Put the “effect” at the far right (the fish’s head)
• Draw a thick “spine” through the middle
• Diagonal “bones” branch off the spine, each labeled with a cause category (Man, Method, Machine/System, Material, etc.)
• Smaller bones branch off each category bone with specific causes

It looks similar to a logic tree, but a fishbone diagram is built around sorting into categories from the start. Instead of writing down whatever causes come to mind, you surface them along fixed angles, which makes it harder to miss a perspective.

The real knack of this technique isn’t the effect (the head) or the individual causes (the small bones) — it’s how you cut the category bones. Once the categories are set, you can surface small bones almost mechanically by asking “what’s the cause from this angle?”

Where this works well

• When you want to surface, without missing anything, the causes behind a single result (a problem, a defect, stalled progress)
• When the causes differ in kind — some about people, some about process — and you want to organize and compare them
• When your team is running a root-cause meeting and you don’t want any one person’s perspective to dominate

How to build it in ThinkTray

Step 1: Write the effect on a card at the far right

Use the Card tool (R) to write the result you want to analyze on a single card.

• Example: “Handling inquiries takes too long”

Step 2: Draw the spine

Use the Line tool (L) to draw one thick arrow pointing from the left toward the effect card.

• This line becomes the “spine.” You can thicken it from the context toolbar’s line-width control

Step 3: Place the category bones — this is the real knack

Place 2–4 cards above and below the spine representing cause categories, and connect each to the spine with a diagonal arrow.

In ThinkTray, a line’s endpoint can attach not just to a card but directly onto another line. Most drawing tools don’t support connecting a line to another line, but ThinkTray does. Since the spine is itself just a line, a bone’s arrow can attach directly to any point along it. Move the spine later, and every bone attached to it follows along.

This is the hardest — and most valuable — step in building a fishbone diagram. The head (the effect) is easy to write, and the small bones (specific causes) come easily once the categories are set, so it’s fair to say this is a technique where you should spend most of your time choosing categories.

Start from a template

4M (Man, Machine, Material, Method) is the classic starting point on factory floors. For a more rigorous pass, add Measurement to get 5M, or Management on top of that for 6M.

But this is a manufacturing-oriented template, so you don’t have to use it as-is. Feel free to rename it to fit your own problem. For customer-facing or support work, “Tools / Systems” often fits better than “Machine,” and “Info / Docs” better than “Material” (the demo above is 4M renamed this way).

If small bones won’t come, question the category

If you set a category and try to write small bones under it but nothing comes to mind, that’s a sign the category doesn’t fit this problem. Don’t force it — try renaming the category, merging it with another, or replacing it with a different angle altogether.

When stuck, write small bones first and name the category afterward (bottom-up)

If you really can’t settle on categories, try reversing the order: freely write down whatever causes (small bones) come to mind without worrying about category, then group similar ones afterward and name the groups (an approach close to the KJ method).

Step 4: Add the small bones (specific causes)

Add cards with concrete causes outside each category card, connected to it with an arrow.

• Aim for 2–3 per category. Too many makes the diagram hard to read
• Example: under “Man” → “Staff lack experience,” “Knowledge is siloed — no one else can cover”

Step 5: Color-code by category (advanced)

Giving a category and the small bones under it the same color makes it obvious at a glance which cause belongs to which category.

• You can change the fill and border color from the context toolbar when a card is selected

Fishbone diagram vs. logic tree

Both break causes down, but here’s a rough guide for choosing between them.

If you’re not sure, a good combo is to surface causes broadly by category with a fishbone diagram first, then use a logic tree to drill further into whichever causes need it.

Tips

• Write the effect concretely — A measurable phrasing like “handling takes too long” surfaces more concrete causes than a vague one like “handling is bad.”
• Cap categories at 4–6 — Too many and the diagram sprawls too wide to take in at a glance.
• If a category yields no small bones, question the angle — When causes won’t come, it’s usually not that you lack perspective — it’s a sign the category doesn’t fit this problem.
• Ask “why?” twice — Asking why a small-bone cause happens, one level deeper, often gets you to a more root cause.
• Separate fact from guesswork — Color-code cards that are “just a guess” differently from confirmed facts, so they’re easy to verify later.

The fishbone diagram (cause-and-effect diagram) was devised by Kaoru Ishikawa in 1956 as a quality-management technique. It’s also known as the Ishikawa diagram. Wikipedia