What it is
Inferring that what is true of the whole must be true of each of its parts.
In the wild
The company is profitable, so every department is.
How to answer it
Ask for the breakdown. Aggregates hide their own variation.
Part and whole
Fallacy of division
Also called Whole to part error
In depth
Origin and naming
The mirror image of the fallacy of composition, and treated with the same lineage: Aristotle sketched it in 'On Sophistical Refutations', and both were formalised under their current names in nineteenth-century logic textbooks. The atomist move — a whole is coloured, so its tiniest pieces must be — is the classic textbook target.
More places it shows up
The dataset contains a billion rows, so each row must be huge.
The choir performed superbly tonight, so our new tenor probably covered himself in glory.
The department is described as flat and agile, so every team inside it must run that way.
The podcast won a national award, so my favourite episode must be among the best.
How to spot it
- Notice when a whole-level label ('world-class hospital', 'well-run system') is handed down to a member with no member-level check.
- Notice when an aggregate figure (average, total, general reputation) does all the talking and no breakdown is ever asked for.
- Notice when the part is described with confidence even though it was never inspected on its own.