Composition

Jason Waller

You like to eat onions, carrots, and beef, right? So, I know you’ll love this casserole made of onions, carrots, and beef that I cooked for you.

The typical mom

The fallacy of composition occurs when one incorrectly infers that the characteristics, attributes, or features of individuals comprising some group will also be found in the group as a whole.

Consider the following:

(1) Each brick in this building is square.

(2) Therefore, this building is square.

The conclusion here clearly does not follow from the premise, thereby making the argument invalid. It is, of course, possible to make a non-square building from square bricks. So from the fact that the bricks are square, we cannot infer that the building must also be. Similarly:

(1) Each brick in this building weighs one pound.

(2) Therefore, this building weighs one pound.

This argument is also clearly fallacious because the weight of a brick will not be the same as the weight of the whole building. From the fact that a part of the building has a certain property (in this example, weighing one pound), it does not follow that the whole building has that property (it weighs much more than one pound.)

The two above arguments are obviously invalid, but there are other argu­ments that are fallacious for the same reason but which are much less obvi­ously invalid. Consider the following:

(1) Congressmen Jones, Mark, and Smith are all radicals.

(2) Therefore, Congress is radical.

It may be tempting to infer that Congress is radical from the claim that Jones, Mark, and Smith are radical. But we cannot infer the radical nature of Congress from this claim alone. Perhaps there are hundreds of other members of Congress who may counteract the radical tendencies of these three. Similarly, consider the following:

(1) John cannot lift the box.

(2) Therefore, John and his brothers cannot lift the box.

This argument is also fallacious for the same reason. We cannot infer anything about whether John plus his brothers can lift a given box from the claim that John alone cannot do it.

Inferences from a part to a whole can be made if additional assumptions are added to guarantee that the whole will have the property if the parts do. For example, if the chapter of a book is made of paper and the book is made of only one kind of material, then we can infer that the whole book must be made of paper. This inference is valid because we added the assumption that the book is made of only one kind of material. Without this assumption, the inference would not have been valid.

The easiest way to avoid this fallacy is never to assume that the character­istics, attributes, or features of individuals comprising some group will also be found in the group as a whole. One must inspect and evaluate the char­acteristics, attributes, or features of the whole separately from the parts of which the whole is comprised.