The part-to-whole flaw
What is true of the parts is not automatically true of the whole.
Fallacy vs. flaw, on this site. Our fallacy page on part-to-whole teaches the general error. This page is the LSAT version: Flaw questions word the right answer as "attributes to the whole a property of its parts" (or the reverse). The testable skill is checking the direction of the move.
Start with the general version: the fallacy page. Then come back here for the test-day version.
What it is
The part-to-whole flaw takes something true of individual members and concludes it is true of the group, or takes something true of the group and applies it to each member. Both directions are flawed.
Parts can have properties the whole lacks (each brick is light; the wall is heavy), and wholes can have properties the parts lack (the team is ranked first; each player is not).
An LSAT-style example
This example is original. It is not a real LSAT question.
Every player on the championship team is an excellent athlete. Therefore the team's coaching staff must be excellent too.
The flaw: Player quality says nothing about coaching quality. The argument moves a property from one part of the organization to a different part entirely.
How to spot it on test day
- Identify the property in the conclusion. Who actually has it in the premises? If the owners differ, flag it.
- Both directions count: parts-to-whole ("each brick is light, so the wall is light") and whole-to-parts ("the company is profitable, so every division is profitable").
- Averages are a common vehicle: a group average tells you almost nothing about any individual member.
The right answer vs. the trap
The right answer
Usually "infers that the whole has a property because its parts do" (or the reverse).
The trap
"The argument generalizes from a small sample." Part-to-whole is not sampling. The evidence can be about every single part and the flaw still stands.
Find your weak flaws
The free diagnostic scores flaw questions separately and shows whether this pattern is costing you points.