Full Idea
The fallacy of composition is an inference relying on the invalid principle that whatever is true of every part is also true of the whole; thus, we cannot assume that because the members of a committee are rational, that the committee as a whole is.
Gist of Idea
The fallacy of composition is the assumption that what is true of the parts is true of the whole
Source
Thomas Mautner (Penguin Dictionary of Philosophy [1996], p.102)
Book Reference
'British Moralists 1650-1800 Vol. 1', ed/tr. Raphael,D.D. [Hackett 1991], p.102
A Reaction
This is a very common and very significant fallacy, which is perpetrated by major philosophers like Aristotle (Idea 31), unlike most of the other informal fallacies.
Related Idea
Idea 31 If bodily organs have functions, presumably the whole person has one [Aristotle]