The fallacy of Composition occurs whenever someone attributes a quality belonging to the parts of a thing to the whole thing itself. This can occur when all of the parts share the quality in question, or even when only some of them do (especially, if there is some reason to over-estimate the relevance of the sampled parts).
The example I learned in my freshman logic class began with the assumption that all the parts used in a car were in perfect working order and concluded that the car would also work just fine, thus ignoring the possibility that the parts had been assembled wrong. We could update this example to computers and it would work the same way.
The converse of this fallacy is Division.
Figurative speech sometimes parallels this fallacy insofar as people sometimes refer to something or someone by referencing a part of that person or things (as in referring to a woman by calling her a ‘blonde; or describing the movements of an army in terms of ‘boots on the ground’). Likewise, people sometimes refer to a whole means of a name for one of its parts. (This occurs when citizens of the United States refer to their country as “America,” and of course we often say of people that they are ‘drinking’ when we actually mean to say that they are consuming an alcoholic beverage.) These metanymic references may be distinguished from fallacies such as composition and division in at least two ways.
- Figurative speech need not entail a literal confusion of the qualities in question whereas the fallacies in question do.
- Both fallacies take the form of an inference from a premise to a conclusion. In the case of composition, the premise will be claim (stated or implied) about the qualities of a part and the conclusion will literally attribute that quality to the whole on the basis of its applicability to the part(s).