False analogy

False analogy is an informal fallacy applying to inductive arguments. It is often mistakenly considered to be a formal fallacy, but it is not, because a false analogy consists of an error in the substance of an argument (the content of the analogy itself), not an error in the logical structure of the argument.

In an analogy, two concepts, objects, or events proposed to be similar in nature (A and B) are shown to have some common relationship with another property. The premise is that A has property X, and thus B must also have property X (due to the assumed similarity of A and B). In false analogies, though A and B may be similar in one respect (such as color) they may not both share property X (e.g. size). Thus, even if bananas and the sun appear yellow, one could not conclude that they are the same size. Many languages have culturally idiosyncratic idioms for invalid analogies or comparisons. Such false analogies are likened to "comparing apples and oranges" in English and to "comparing apples and péars" in Dutch. In Serbian, a false analogy is likened to "comparing grandmothers and frogs."

Examples

• The following is an example of a false analogy:

The universe is like an intricate watch.

A watch must have been designed by a watchmaker.

Therefore, the universe must have been designed by some kind of creator.

While the universe may be like a watch in that it is intricate, this does not in itself justify the assumption that watches and the universe have similar origins. For this reason, some scientists and philosophers do not accept the analogy, known as the argument from design, with this one specifically known as The Watchmaker Analogy.

By changing a term, the fallacy becomes apparent:

The universe is like an intricate watch.

Many early watches were designed by locksmiths.

Therefore, the universe may have been designed by some kind of locksmith.

The structure of the argument is similar, but here we can more easily see the evolution of watches in terms of less complex mechanisms and tools. The false analogy becomes more apparent in terms of comparing locks to watches, and locks to the universe.

Incorrectly classifying an analogy false

Very often people try to refute a correct analogy as a false analogy, often saying "Well, but that's different because", and refer to an existing property that the two things in the analogy indeed do not share. In cases like this, such a refutation is merely a "false charge of fallacy". But as analogies are comparing two different things there are always some properties that A and B do not share, so it is tempting to pull up one such difference to try to disqualify the analogy. For the purposes of the analogy, however, it is important to check if that difference is relevant for the analogy or not.