How sure people say they are
Eight expressions. Match each to where it sits — and notice that only two of them are actually about evidence.
The case file
On a Tuesday in March, a book was found in the returns box of a city library. It had been borrowed on 4 May 1994, from a branch that closed in 2011. Thirty-one years.
The library would like to know who returned it. So would you.
Nine things that are true
| # | Evidence |
|---|---|
| 1 | The book is a field guide to British birds, 1971 edition. Date stamp: 4 May 1994. |
| 2 | It was in the returns box on Tuesday morning, not posted. The box is emptied at 09:30 and was empty at 17:00 on Monday. |
| 3 | The counter is unstaffed until 09:30. No fine was paid, and no fine was ever going to be charged on a branch closed in 2011. |
| 4 | Inside: a boarding-pass stub, Manchester to Dublin, 12 June 1994. The name has been torn off, carefully, along a fold. |
| 5 | A pressed oak leaf between pages 142 and 143 — the pages on the jay. |
| 6 | A shopping list in two different hands. One reads "batteries, bread, film". Under it, in a rounder hand: "cards for Mum". |
| 7 | A bookmark from Wilson’s Bookshop, which closed in 1998. |
| 8 | A note in blue ink, on library-issue paper from the counter: "I’m sorry it took so long. — M". |
| 9 | The borrower’s card was registered to a student hall of residence. The library will not release the name. |
Three questions. Check what the file actually says.
1. What does item 2 establish?
2. What does item 8 tell you that item 4 does not?
3. Item 4: the name has been torn off carefully, along a fold. What does carefully add?
A claim in one breath
The shape you will use forty times in the next half hour:
Whoever returned it [modal] have been at the library that morning, because the note is on counter paper — although somebody could have taken the paper away and brought it back.
Claim, evidence, and the thing that weakens it. A claim with no third part is a claim nobody has tested.
Four questions. Each is a claim somebody might make from this file.
1. "Whoever returned it ___ have been in the building on Tuesday morning." (the note is on counter paper)
2. Why not must in the question above?
3. "The book ___ have been posted." (item 2)
4. "M ___ be the borrower." (item 9 gives no name)
Six claims, graded
Two to four words per gap. Take the strongest form the file will support — and no stronger.
The book posted, because item 2 rules that out. Whoever brought it the library before, since they knew where the returns box was. The leaf pressed by the borrower in 1994, or by anybody since. The torn boarding pass an accident — the file says it was torn along a fold, carefully. The two hands on the shopping list the same person, and the second hand somebody younger.
Six claims from a group that got carried away. Each is grammatical. Each claims more than the file allows.
1. M must be the borrower’s daughter.
2. The borrower must have died, and somebody found the book in the house.
3. The trip to Dublin must have been a holiday.
4. They mustn’t have wanted to be seen, so they came before 09:30.
5. The oak leaf proves they were interested in birds.
6. The bookmark shows they bought the book at Wilson’s. — it is a library book
Build it, then defend it
How the twenty-six minutes run. Groups of three. Eight minutes building, eight minutes cross-examining the group next to you, six minutes for the final account, four for moving between them.
Stage 1 · Groups of three · 8 minutes
Build the best account of who returned the book and why, using only the nine items.
Six claims, each with a modal you can defend and the evidence named in the same sentence.
- Sort the nine items first: which eliminate, which suggest, which are decoration?
- Every claim gets said in the three-part shape: claim, evidence, and what weakens it.
- Mark your one must. You are allowed one. Choose it carefully.
- Name the question you would ask the library if they would answer one.
Stage 2 · Cross-examination · 8 minutes
Swap with the group beside you. Their account is now yours to test, and yours is theirs.
Four minutes each way. Break one claim, and improve one.
- Challenge their must first: what rules out the alternatives?
- Find one claim that is weaker than the evidence allows — those exist too, and they are worth more than the overreaches.
- Use that’s a stretch and I wouldn’t rule it out. They are the tools for this, and they are not rude.
- Do not defend by repeating. Defend by naming evidence, or downgrade.
Stage 3 · The final account · 6 minutes
Back in your own group. Rewrite the account with everything the cross-examination did to it.
Four claims, correctly graded, and one sentence for the library’s newsletter.
- Downgrade anything that could not answer a challenge. Upgrade anything you had hedged unnecessarily.
- State plainly the one thing your account cannot explain.
- The newsletter sentence is one sentence, for the public, and it must not claim more than you can defend.
- Read it out. The room votes on whether it overclaims.
What the newsletter sentence showed
Two questions.
1. What happened to most groups’ single must under cross-examination?
2. Which is easier to hear: an overclaim in discussion, or an overclaim in a written sentence for strangers?
Graded, not guessed
Two questions. Twenty seconds.
1. What are the three parts of a defensible claim?
2. Why is an underclaim worth finding too?
Next. Why none of this ever gets corrected — and what your own claims sound like to somebody who was not in your head.