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Advanced Assumption Listing

find the stone the whole arch leans on

A big decision is an arch of premises, some of them never said out loud. List them all, with the people deciding with you. Rate each one, find the keystone that would bring the conclusion down, and decide in advance what you'd see first if it started to slip.

  • Challenging to start
  • Life-Changing impact
  • Learn it in 30 days
  • An hour or two a decision
one conclusion, and the stones it stands on
An arch of assumptions, with a keystone, over the conclusion “we can afford 14 Elm Road” The conclusion sits in the doorway of an arch: we can afford 14 Elm Road, £1,560 a month at a 4.5% fixed rate. Seven stones make the arch. Solid: the deposit is ours, and the commute is bearable. With caveats: no big repairs in year one, childcare costs what it does now, and we'll stay at least five years. Unsupported: rates stay under 6.5% when the fix ends, and the keystone, both incomes carry on. If the keystone goes, the payment is 40% of Alex's take-home, or 48% if rates reach 6.5%. Signposts: ask about Sam's contract renewal by 1 March, and get remortgage quotes at month 20. The check is rerun at the offer, the survey and exchange. We can afford 14 Elm Road £1,560 a month, 4.5% fixed for two years 1 2 ? 3 ? K 4 5 6 solid with caveats ? unsupported the keystone if it goes, so does the arch on Alex's pay alone: 40%, 48% if rates reach 6.5% signposts K Sam's renewal: ask by 1 March 3 remortgage quotes at month 20 recheck at offer survey exchange
  1. 1

    The deposit is ours · solid

    It's in savings, not promised.

  2. 2

    No big repairs in year one · with caveats

    The survey flagged the roof. Signpost: A roofer's quote before exchange.

  3. 3

    Rates stay under 6.5% when the fix ends · unsupported

    Nobody knows; we picked a number. Signpost: Remortgage quotes at month 20.

  4. K

    Both incomes carry on · keystone, unsupported

    Sam's contract ends in June. Signpost: Ask about renewal by 1 March.

  5. 4

    Childcare costs what it does now · with caveats

    Fees rose last spring. Signpost: The nursery's fee letter in April.

  6. 5

    We'll stay at least five years · with caveats

    Unless Alex's office moves.

  7. 6

    The commute is bearable · solid

    We both did it twice at rush hour.

For a decision that's hard to undo

Check the arch before you walk under it.

A house, a move, a new job, a business. Something with a date you'll commit on, and people who decide it with you.

  1. Write the conclusion as one sentence

    Not the question, the answer you're leaning towards: “we can afford 14 Elm Road”, not “should we buy?”. The check is of a line you're about to act on.

  2. List alone, then together

    Each of you spends ten minutes writing every premise under that sentence, the ones nobody says too. Then put the lists side by side. The lines only one of you wrote are the ones you'd never have checked.

    Stuck? Ask what someone who disagreed would have to be right about.

  3. Ask each one why it must be true

    How sure are we, and what is that based on? What could undermine it? Was it true once and less so now? Rate it solid, with caveats, or unsupported.

  4. Find the keystone

    For each stone: if it turned out false, would the conclusion fall, or just get worse? The ones that would bring it down are the keystones. Usually there are one or two. Run the numbers without them.

  5. Give it a signpost

    For each keystone and each unsupported stone, write what you'd see first if it were failing, and a date to look. A signpost turns a worry into an appointment.

  6. Recheck before each commitment

    Read the list again at every point of no return: the offer, the survey, the signature. Change a rating when something new comes in. Over a month, run this on one real decision, start to finish.

Taking a job in another city? Conclusion: “this is a step up.” Keystone: “the team I met is the team I'll join.” Signpost: ask, in writing, who you'd report to on day one, before you resign.

The Primer's own example

Five assumptions. Which held?

During the sniper shootings around Washington, DC in October 2002, a working picture formed quickly: a single white male with some military training, driving a white van. The CIA's A Tradecraft Primer uses the case to show the key assumptions check: break the picture into its parts and rate each one. Here are its five, with the Primer's ratings. Guess which held, then see.

  • The sniper is a man.

    Highly likelybut not certain, given past precedent with serial killers.

  • The sniper is acting alone.

    Highly likelybut not certain, given past precedents.

  • The sniper is white.

    Likelybut not as certain, given past precedents.

  • The sniper has military training.

    Possiblebut not sufficient reason to rule out suspects who have had none.

  • The sniper drives a white van.

    Possiblea credible eyewitness, but more than 70,000 white vans are registered in the Maryland suburbs, and other vehicles are being described.

The two men were arrested on 24 October 2002, asleep in that Caprice at a rest stop in Maryland. “Acting alone” was rated highly likely, and it was wrong. A rating doesn't make an assumption true; writing it down is what lets the next tip contradict it. Without that, the Primer says, contradicting information often gets “lost in the noise”.

Try it on yours

Run the check.

Write the conclusion, then the stones under it. Rate each one, mark the keystone, and give the risky ones a signpost and a date. The sheet builds the arch and tells you what's missing.

    your conclusion

      Nothing you type is saved or sent anywhere. Copy the check before you leave the page.

      The idea

      Why it works.

      The assumptions that hurt are the ones nobody chose. They arrive with the first version of the plan and set like mortar. Listing them one by one turns the conclusion back into parts, and each part can be asked the question the whole never is: why must this be true?

      The keystone is where the work pays. Most premises, if wrong, make a decision worse. One or two make it wrong. Finding those, and agreeing in advance what would warn you, is how a couple, a team or an analyst changes their mind early instead of late.

      When to stop

      Know when not to.

      • Not for choices you can undo. If a mistake costs a week, try it instead of checking it.
      • Stop at the ones that change the decision. A stone that couldn't move the conclusion doesn't need a signpost.
      • Don't let it become a veto. Every plan has unsupported stones. The aim is to watch them, not to wait until there are none.
      • Recheck, don't restart. At each commitment, read the list and update ratings. A new list each time loses the history.

      Go deeper

      Keep going.

      Practise this in HourLife.

      In Decisions: Assumptions. Write down a decision, weigh the options, mark the one you chose, and come back later to record how it turned out.

      Download on the App Store Download on the Mac App Store How Decisions works in HourLife