A close view of the head of a raven, Corvus species

Weak Analogy

Alias:

  • False Analogy
  • Faulty Analogy
  • Questionable Analogy

Type: Informal Fallacy

Form:

A is like B.
B has property P.
Therefore, A has property P.
(Where the analogy between A and B is weak.)

Example:

Efforts to ban chlordane assailed

WASHINGTON (AP)--The only exterminator in Congress told his colleagues Wednesday that it would be a short-sighted move to ban use of chlordane and related termiticides that cause cancer in laboratory animals.

Supporters of the bill, however, claimed that the Environmental Protection Agency was "dragging its feet" on a chemical that could cause 300,000 cancers in the American population in 70 years.

"This bill reminds me of legislation that ought to be introduced to outlaw automobiles" on the grounds that cars kill people, said Rep. Tom DeLay, R-Texas, who owns an exterminating business.

EPA banned use of the chemicals on crops in 1974, but permitted use against termites because the agency did not believe humans were exposed. Chlordane does not kill termites but rather drives them away.

Source: Associated Press, June 25th, 1987

Analysis

Exposition:

This is a very common fallacy, but "False Analogy", its common name, is very misleading. Analogies are neither true nor false, instead they come in degrees from near identity to extreme dissimilarity. Here are two important points about analogy:

  1. No analogy is perfect, that is, there is always some difference between analogs. Otherwise, they would not be two analogous objects, but only one, and the relation would be one of identity, not analogy.
  2. There is always some similarity between any two objects, no matter how different. For example, Lewis Carroll once posed the following nonsense riddle:

    How is a raven like a writing desk?

    The point of the riddle was that they're not; alike, that is. However, to Carroll's surprise, some of his readers came up with clever solutions to the supposedly unsolvable riddle, for instance:

    Because Poe wrote on both.

Some arguments from analogy are based on analogies that are so weak that the argument is too weak for the purpose to which it is put. How strong an argument needs to be depends upon the context in which it occurs, and the use that it is intended to serve. Thus, in the absence of other evidence, and as a guide to further research, even a very weak analogical argument may be strong enough. Therefore, while the strength of an argument from analogy depends upon the strength of the analogy in its premisses, it is not solely determined by that strength.

Subfallacies:

Resources:


Analysis of the Example:

Representative DeLay attempts to argue against a bill banning chlordane by comparing it to a bill banning automobiles, but this analogy is very weak. Here are some of the relevant differences:

  • Banning automobiles would be economically and socially disruptive in a way that banning a single pesticide would not.
  • There are many alternative pesticides available to replace a banned one, but there are few modes of transportation available which could replace cars.
  • Automobiles play a significant role in our society, whereas chlordane was used only to prevent termite damage to houses, which is of comparatively minor importance.

Acknowledgment:

The photographic print of the head of a raven is available from AllPosters.


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