False analogy

A False Analogy is a faulty instance of the Argument from analogy.

The Argument from Analogy

The process of analogical inference involves noting the shared properties of two or more things, and from this basis inferring that they also share some further property. The structure or form may be generalized like so:

P and Q are similar in respect to properties a, b, and c.

Object P has been observed to have further property x.

Therefore, Q probably has property x also.

False Analogy

Several factors affect the strength of the argument from analogy:

The relevance of the known similarities to the similarity inferred in the conclusion.

The amount and variety of the examples in the analogy.

The number of characteristics that the things being compared share.'

An argument from analogy is weakened if it is inadequate in any of the above respects. The term "false analogy" comes from the philosopher John Stuart Mill, who was one of the first individuals to engage in a detailed examination of analogical reasoning. One of Mill's examples involved an inference that some person is lazy from the observation that his or her sibling is lazy. According to Mill, sharing parents is not all that relevant to the property of laziness.