The fallacy of composition arises when one infers that something is true of the whole from the fact that it is true of some part of the whole (or even of every proper part). For example: “This fragment of metal cannot be broken with a hammer, therefore the machine of which it is a part cannot be broken with a hammer.” This is clearly fallacious, because many machines can be broken into their constituent parts without any of those parts being breakable.
This fallacy is often confused with the fallacy of hasty generalization, in which an unwarranted inference is made from a statement about a sample to a statement about the population from which it is drawn.
The fallacy of composition is the converse of the fallacy of division. The fallacy of composition is also known as the “un-ecological fallacy.”
- Human cells are invisible to the naked eye.
- Humans are made up of human cells.
- Therefore, humans are invisible to the naked eye.
In Keynesian macroeconomics, the “paradox of thrift” theory illustrates this fallacy: increasing saving (or “thrift”) is obviously good for an individual, since it provides for retirement or a “rainy day,” but if everyone saves more, Keynesian economists argue that it may cause a recession by reducing consumer demand.
In voting theory, the Condorcet paradox demonstrates a fallacy of composition: Even if all voters have rational preferences, the collective choice induced by majority rule is not transitive and hence not rational. The fallacy of composition occurs if from the rationality of the individuals one infers that society can be equally rational. The principle generalizes beyond the aggregation via majority rule to any reasonable aggregation rule, demonstrating that the aggregation of individual preferences into a Social welfare function is fraught with severe difficulties (see Arrow’s impossibility theorem and Social choice theory).
Modo hoc fallacy
The modo hoc (or “just this”) fallacy is the informal error of assessing meaning to an existent based on the constituent properties of its material makeup while omitting the matter’s arrangement. For instance, metaphysical naturalism states that while matter and motion are all that comprise man, it cannot be assumed that the characteristics inherent in the elements and physical reactions that make up man ultimately and solely define man’s meaning; for, a cow which is alive and well and a cow which has been chopped up into meat are the same matter but it is obvious that the arrangement of that matter clarifies those different situational meanings.