Part to Whole
A fact about a part does not prove it of the whole.
What it is
Part to whole takes a fact about one part and treats it as true of the entire group. The reverse move, whole to part, takes a fact about a group and forces it onto one member. Both are the same mistake: assuming parts and wholes behave alike.
Teams, machines, and economies have properties that none of their parts have alone. That is where this flaw lives.
An LSAT-style example
This example is original. It is not a real LSAT question.
Every component of the new transit system was built under budget. Therefore the transit system as a whole came in under budget.
The flaw: Parts being under budget does not prove the whole project was. Integration, labor, and delays live at the level of the whole, not the parts.
How to spot it on test day
- The evidence is about pieces. The conclusion is about the group.
- Ask: does this property actually transfer from part to whole? Weight transfers. Budget discipline does not.
- Watch for the reverse too: a fact about a group applied to one member.
The right answer vs. the trap
The right answer
The correct answer says the argument wrongly assumes what is true of the parts is true of the whole.
The trap
The trap may describe a hasty generalization instead. The difference: here the evidence can be complete about the parts and still fail, because wholes have their own properties.
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