Thinking Lab · 4 lessons

Critical Thinking

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Evaluate claims and evidence

In one line: Say exactly what would have to be true for a claim to hold — then find out whether it is.

When you need it

• Someone is asking you to act on a claim: buy, switch, commit, believe.
• A statistic arrives without the question it was meant to answer.
• Everything you have read on a subject agrees, and you have only read one kind of source.

The common misreading

What people think

Critical thinking means being sceptical and disagreeing more.

What is true instead

It is symmetrical. The same test is applied to the claim you like, and most people only run it on the ones they do not.

After this module you can name the one piece of evidence that would settle a claim — or notice that none exists.

The key idea

Critical thinking is not disagreeing with things. It is the ability to say exactly what would have to be true for a claim to hold — and then to check.

Start with a hard question

Something everyone around you says as if it were settled. Write it down and then write what evidence would actually settle it.

What is a widely repeated claim in your field that you have never seen evidence for?

Answer it before reading the lessons — then again after, and notice what changed.

The lessons

• Claims, evidence and sources — For any claim worth acting on, write down what evidence would settle it. Often the answer is "none available", and that is the finding. (6 min)
• Assumptions, arguments and counterarguments — The assumptions nobody stated are where arguments usually fail, and they are findable in about two minutes. (6 min)
• Correlation, confirmation, and cherry-picking — An anecdote establishes possibility, never frequency. Almost every misleading claim lives in that gap. (7 min)
• False dilemmas and strawmen — When you are offered exactly two options, the most valuable question is what the third one is. (5 min)

Practise it

Short exercises. Under each is what a considered answer tends to contain — not a mark scheme.

Spot the unsupported claim

"Remote teams are 20% less productive. Every manager I have spoken to says the same. We should bring everyone back." What is being claimed, what is offered as support, and what is missing?

• Tends to contain: A precise number with no source
• Tends to contain: Managers as a sample, and who is missing from it
• Tends to contain: Productivity is never defined
• Tends to contain: Even if true, the conclusion does not follow automatically

Correlation or cause

A city notes that neighbourhoods with more libraries have higher exam results, and proposes building libraries to raise results. What are three other explanations?

• Tends to contain: A common cause such as income or council spending
• Tends to contain: Reverse direction: results attract investment
• Tends to contain: Selection: who lives near libraries
• Tends to contain: What would need to be measured to tell these apart

The missing evidence

A product page says "trusted by over 500 companies". What would you need to know before that means anything to you?

• Tends to contain: Companies like yours, or any companies
• Tends to contain: Still using it, or ever signed up
• Tends to contain: What "trusted" is standing in for
• Tends to contain: Who left, and why

Compare two arguments

A: "We should stop the project — we have spent six months and it is not working." B: "We should continue — we have spent six months." Which reasoning is sounder, and what does each actually rest on?

• Tends to contain: Both cite the same six months for opposite conclusions
• Tends to contain: Money and time already spent cannot be recovered by continuing
• Tends to contain: The only relevant question is what happens from here
• Tends to contain: Neither states what "not working" means

Reflect

What did you believe at the start of this week that you now hold more loosely, and what caused that?