description

The Fallacy of Composition is the failure to accept that what is true for components of a system may not be true for the system.

Arguably, it's a special case of hasty generalization, but I've listed it seperately because it is so important.

examples

"Since I can see the concert better by standing on my seat, it follows that if everybody stood on their seats, we would all have a better view."

"The person who gets a gold medal is happy; it follows that if everybody got gold medals, they would all be happy."

"Phil and Mary are excellent singers; they will form an excellent duo."

"Every member of the hockey team is excellent; the team will be excellent."

"A person who pursues his best interests at the expense of others is better off than one who does not; it follows that if everybody pursued a policy of their own interests at the expense of others, we would all be better off." (note: in economics, this is referred to either as the theory of ethical egoism as championed by Ayn Rand who believes this is actually valid, or the Tragedy of the Commons by most people who recognize this as a fallacy)

"Cars create less pollution than buses, so if we all drove cars there would be less pollution than if we all rode buses."

"Because everything in the universe has a prior cause, the universe itself must have been caused by something that existed previously."

further discussion

This fallacy is very difficult to identify because it follows a pattern that is often valid. It depends on our knowledge about the world to notice that light car parts can add up to a heavy car. Consider these invalid arguments:

"All parts of the car are small and easy to carry, therefore the car must be small and easy to carry"

"Atoms in a penny are too small to see, therefore a penny must be too small to see."

Now, compare to these valid arguments in the same form:

"All parts of the car are white, therefore the car must be white."

"All atoms in the penny are copper, therefore the penny must be copper."

We just happen to know through experience that small objects add up to big objects and light objects add up to heavy objects, whereas copper objects add up to another copper object and white objects add up to another white object.