Argument from silence


The fictional detective Sherlock Holmes, created by Arthur Conan Doyle, used this argument in a story called The Adventure of Silver Blaze. While reviewing the evidence of the case with Watson and  Scotland Yard Detective Gregory, Holmes raises "the curious incident of the dog in the night-time." Gregory replies "The dog did nothing in the night-time." and Holmes points out that "That was the curious incident." Holmes had deduced that the dog made to noise because there was not stranger to bark at. The horse, Silver Blaze, had been stolen by someone the dog knew. Holmes built his argument on the silence of the dog and solved the case.  Another example of the argument from silence is the assertion that Marco Polo did not go to China. His travel journals do not mention the Great Wall of China and some people argue that anyone who explored China would mention something as significant as the Great Wall.

Name of fallacy Argument from silence
Type Inductive Logic Argument, Informal Argument
Description A conclusion based on silence or lack of contrary evidence.
Example John: Do you know any Spanish?
Jack: Of course. I speak it like a native.
John: That's good, because I need to know the Spanish phrase for "Happy Birthday".
Jack: Sorry, I don't have time for that right now. Maybe tomorrow. Bye.

Afterwards, Jack continually refuses to give John the Spanish translation, either by ignoring John or by giving excuses. John then concludes, by argument from silence, that Jack does not in fact know Spanish or does not know it well. In other words, John believes that Jack's ignorance is the most plausible explanation for his silence. Use of argument from silence in this situation is reasonable given the alternatives, that Jack either doesn't want or is afraid to translate, would be unreasonable without more information.
Treatment Explore reasons why the subject would not answer the question. There may be a good reason and this could invalidate the conclusion from lack of evidence.