Logic Topics
Fact, Opinion, and Inference
The first step in reasoning well is pulling apart three things that always arrive mixed together. A fact can b…
The Law of Identity
The law of identity: within one discussion, a term has to keep one meaning. A team debating “improve performan…
The Law of Non-Contradiction
A claim and its negation cannot both hold at the same time, about the same thing, in the same sense, under the…
The Law of Excluded Middle
For a claim with a clear boundary, under fixed conditions it either holds or it does not — there is no third s…
Deduction, Induction, and Analogy
Three basic ways of reasoning. Deduction moves from a general rule to a specific conclusion, and when the prem…
Claim, Evidence, and the Link Between Them
Three checks for any argument. (1) What exactly is the conclusion — what do they want you to believe? (2) Is t…
Sufficient and Necessary Conditions
A sufficient condition (if A then B): when A holds, B must hold. Only two moves are valid — affirming the ante…
Syllogism
A syllogism is the tool that connects a general rule to a specific fact. Major premise (the rule): “Projects w…
Deductive Closure: From Opinion to Action Plan
Five steps that turn an opinion into something executable and checkable. (1) State the conclusion as a specifi…
Competing Hypotheses
When information runs out, the first explanation that comes to mind is usually just the one that best fits you…
The Four Pitfalls of Induction
Induction looks for what several specific facts have in common and forms a judgement over a wider range; the c…
The Five-Step Induction Method
Five steps for turning scattered experience into a judgement you can rely on. (1) State the question precisely…
Correlation and Causation
Two things moving together does not make either the cause of the other. Ice-cream sales and drowning accidents…
Root Cause and the Causal Chain
Causes come in three layers: the surface cause (the warehouse didn’t ship), the intermediate cause (the wareho…
Six-Step Causal Analysis
Six steps. (1) Define the outcome precisely — object, period, magnitude: “sales of this product in the Southea…
Second-Order Thinking
First-order thinking sees only the immediate result of an action: cut the price and volume rises; assert autho…
Perverse Incentives
Rules change incentives, incentives change behaviour, and behaviour then swallows what the rule was for. In ma…
The Pyramid Principle
The Pyramid Principle is four moves. (1) Answer first — open the meeting with your recommendation, open the em…
Structured Communication and SCQA
Five steps to build a pyramid in three minutes. (1) Decide who you are talking to and what they care about — y…
Red Herring and Straw Man
A red herring replaces the original question with one that is easier to prove or more emotive. Asked why there…
Ad Hominem and Appeals to Motive
An ad hominem attacks the character, identity, or motive of the person asking instead of answering the questio…
Appeals to Authority, Popularity, and Tradition
Substituting standing, popularity, history, or good intentions for evidence. Appeal to authority — “the expert…
False Dilemma
A false dilemma compresses a complicated question into two options and forces a choice between them. A princip…
The Slippery Slope
A slippery slope asserts that once A happens you slide all the way to a catastrophic Z, without showing that a…
Reasoning by Analogy: A Four-Step Method
Analogy notices that two things resemble each other in some respects and infers that they may resemble each ot…
Spotting a False Analogy
Six questions for catching a bad analogy. (1) What conclusion is the analogy meant to establish? (2) Does the …
Means and Ends
An end is the result you actually want — income, health, being trusted. A means is what you do to get there — …
A Checklist for Big Decisions
Seven checks for a decision that matters. (1) Write the goal concretely, not as a slogan. (2) List the means c…