A weak analogy fallacy is a part of informal logic. The fallacy can be found in the content of the argument. As the name suggests, it occurs when comparing two similar things. More so, when drawing a conclusion from a comparison of objects that share a similarity.
The logical form of a weak analogy fallacy in an argument:
- Example X is relevantly similar to example Y.
- P follows from X.
- Therefore, P follows from Y
(Robert Arp, Steven Barbon, Michael Bruce. Bad Arguments. Wiley Blackwell, 2019)
There’s nothing wrong with the form of the argument, per se. If X and Y really do share the properties relevant to the drawn conclusion, the analogy won’t cause difficulty in the argument. In that case, the analogy won’t be weak. However, if the similarity between X and Y is not valid in reality(experience) the analogy is weak. The same applies if the similarity has no clear connection to the drawn conclusion.
The drunk man is often compared with the madman. Although there is a reason why being drunk is compared with a disability, a weak analogy fallacy is made. Saying that the drunk man and the madman are similar in some way is not fallacious per se. However, jumping to a conclusion from the comparison is certainly a fallacy.
“Drunkenness and insanity are the same, both affect the mind in a similar way”
In the example, the speaker is stating that there’s no distinction between drunkenness and insanity.
The form of the argument is:
- Drunkenness makes a man act insane/ affects a man’s mind
- A mental disability affects the man in a similar way
- Drunkenness and a mental disability are the same thing
The error is obvious. While it’s true that a drunk man differs in behaviour from a sober man, he is not the same as a mentally disabled person. While the disability can’t be cured, drunkenness is only a temporary state. A drunk man can sometimes control himself, a mentally disabled person can’t. Also, drunkenness is really a mild state, while a disability is often extreme.
Weak analogy fallacies can be often found in conspiracy theories too.
A common example is:
“The government is known for misleading the people, the moon landing is fake”
Or:
- The government lies
- The moon landing was a government project
- The moon landing is a lie
While it’s quite true that every form of government has told a lie, it doesn’t necessarily follow that the moon landing is a lie. When you take a look at the actual situation, the USA government has lied where the truth would hurt the public. Also, most of those situations were internal affairs. Apollo 11 was a mission that included scientists, it was an achievement not only for the USA government but mankind as a whole.
Additional information:
Some logicians say that the analogies should only be made between objects of the same class.
- All triangles have 3 angles.
- An obtuse triangle has 3 angles.
The comparison is between all triangles and an obtuse triangle. An obtuse triangle is a subordinate class from the class triangles.