Why Sherlock Holmes isn’t deducting anything

Right now, the bestselling book in our shop isn’t on philosophy. It’s on metacognition. Schools worldwide are keen to learn more about metacognitive strategies after the EEF found it to be “very high impact for very low cost based on extensive evidence”.

So this week, an activity from said book – Thinking Moves A-Z, which, for the first time, makes metacognition simple for teachers and students alike.

Inferences – a quick user’s guide

The Thinking Moves framework breaks down thinking into 26 memorable building blocks, one for each letter of the alphabet. Today, we focus on a philosophical move: Inference.

To infer is to draw a conclusion, usually from some premises (the earlier steps in an argument), a bit like a detective. 

There are deductive inferences – logical, valid steps from premise to conclusion. “If the premises are true, the conclusion must be true.”

All fish can swim.
Fred is a fish.
Therefore, Fred can swim.

Then there are inductive inferences. These are predictions based on past experience. “This has been true every time, so it’s probably true this time.”

Every fish and chip shop I’ve visited offers salt and vinegar

Therefore, all fish and chip shops offer salt and vinegar.

There are also abductive inferences, forming a conclusion from some incomplete evidence. 

There’s a long queue outside the fish and chip shop.
Therefore, they probably sell quite tasty fish and chips.

Sherlock Holmes talks about deduction, but it’s usually abductive inferences he is doing: “You went to the post office, but you have not written a letter, therefore you were likely sending a telegram.” His sense of deduction is more like the mathematical sense – taking away other explanations to get to the true one. 

Inference activity: Solid, shaky, shouldn’t.

Give students the inferences below (they’re all inductive or abductive ones, arguing from observation) and ask them to indicate if they think the conclusion is…

Solid – thumb up
Shaky – thumb wobbling
or Shouldn’t follow – thumbs down.

  • There’s washing on the line. Therefore, someone has recently washed their clothes.
  • The chocolate factory has exploded. Therefore, it will be raining chocolate.
  • Every dog I meet is friendly. Therefore, all dogs are friendly.
  • People are always on their phones. Therefore, phones make people happy.
  • I can see a field of white sheep. Therefore, all sheep are white.
  • There’s frost outside. Therefore, it’s cold outside.
  • There’s hissing venomous vipers in that box. Therefore, we shouldn’t open it.
  • That person looks a bit scruffy. Therefore, they don’t care for their appearance.

You can play this game live during a P4C enquiry. First, notice when a child makes an inference. As Pete Worley of The Philosophy Foundation points out, children naturally give their conclusion first, then their premises (in the form of reasons):

Conclusion: “The mind is not the same as the brain because…
Premise: The mind is inside the brain
Premise: …And if something is inside the other, it can’t be identical to the other.”

You’ll probably need to reverse their order so the reasons come first, conclusion second – and ask everyone to give a hand signal to show whether it’s a solid inference, assuming the premises are true. You’re not asking them if they agree with everything that’s been said, but if the steps are logical. Learn more about the difference between validity and truth with Pete’s brilliant article “Being wrong in the right way”.

For more activities on Inferring, and 25 other distinct acts of thinking – buy Thinking Moves A-Z in our shop.

Opportunity for a London/South East school

We’re busy designing a new Thinking Moves website, launching soon. To help, we need some photos of its metacognitive strategies in action. But alas, the age-old problem of photo permissions. So we’re looking for a school in London, or not far from it, who would be interested in a morning of metacognition workshops (with a stonking discount) in exchange for permission to take photographs for our promotional materials. Preferably soon after half-term. We have all the parental forms ready, so it’s minimal faff for the school. It’ll be first confirmed first served, so please hit reply or email tom@thephilosophyman.com to express your interest.

Best wishes

Tom and Jason

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