Affirming A Disjunct
Affirming a disjunct is a fallacy when in the following form:
- A is true or B is true.
- B is true.
- Therefore, A is not true.*
The conclusion does not follow from the premises as it could be the case that A and B are both true. This fallacy stems from the stated definition of or in propositional logic to be inclusive.
An example of affirming a disjunct would be:
- I am at home or I am in the city.
- I am at home.
- Therefore, I am not in the city.
While the conclusion may be true, it does not follow from the premises. For all the reader knows, the declarant of the statement very well could have her home in the city, in which case the premises would be true but the conclusion false. This argument is still a fallacy even if the conclusion is true. However, this statement is false because the initial premise is false, there are many possible places other than home or the city.
- Note that this is only a logical fallacy when "or" is inclusive. If the two possibilities in question are mutually exclusive, this is not a logical fallacy. For example
- The light is either on or off.
- The light is off.
- Therefore the light is not on.
Read more about this topic: Non Sequitur (logic)
Famous quotes containing the words affirming a and/or affirming:
“In the first place, all books that get fairly into the vital air of the world were written by the successful class, by the affirming and advancing class, who utter what tens of thousands feel though they cannot say.”
—Ralph Waldo Emerson (1803–1882)
“The dissident does not operate in the realm of genuine power at all. He is not seeking power. He has no desire for office and does not gather votes. He does not attempt to charm the public, he offers nothing and promises nothing. He can offer, if anything, only his own skin—and he offers it solely because he has no other way of affirming the truth he stands for. His actions simply articulate his dignity as a citizen, regardless of the cost.”
—Václav Havel (b. 1936)