Argument from ignorance (from Latin: argumentum ad ignorantiam), also known as appeal to ignorance (in which ignorance represents "a lack of contrary evidence"), is a fallacy in informal logic. It asserts that a proposition is true because it has not yet been proven false or a proposition is false because it has not yet been proven true. This represents a type of false dichotomy in that it excludes the possibility that there may have been an insufficient investigation to prove that the proposition is either true or false. It also does not allow for the possibility that the answer is unknowable, only knowable in the future, or neither completely true nor completely false. In debates, appealing to ignorance is sometimes an attempt to shift the burden of proof. In research, low-power experiments are subject to false negatives (there would have been an observable effect if there had been a larger sample size or better experimental design) and false positives (there was an observable coincidental effect). The term was likely coined by philosopher John Locke in the late 17th century.
Often seen in anecdotal evidence, superstitions, correlation-causation fallacies, and experiments with small sample size
These examples contain or represent missing information.
These examples have the potential for "false negative" results.
Main article: Evidence of absence
These examples contain definite evidence that can be used to show, indicate, suggest, infer or deduce the non-existence or non-presence of something.
(Draws a conclusion based on lack of knowledge or evidence without accounting for all possibilities)
Appeal to ignorance: the claim that whatever has not been proven false must be true, and vice versa. (e.g., There is no compelling evidence that UFOs are not visiting the Earth; therefore, UFOs exist, and there is intelligent life elsewhere in the Universe. Or: There may be seventy kazillion other worlds, but not one is known to have the moral advancement of the Earth, so we're still central to the Universe.) This impatience with ambiguity can be criticized in the phrase: absence of evidence is not evidence of absence.
Contraposition is a logically valid rule of inference that allows the creation of a new proposition from the negation and reordering of an existing one. The method applies to any proposition of the type If A then B and says that negating all the variables and switching them back to front leads to a new proposition i.e. If Not-B then Not-A that is just as true as the original one and that the first implies the second and the second implies the first.
Transposition is exactly the same thing as Contraposition, described in a different language.
Null result is a term often used in science to indicate evidence of absence. A search for water on the ground may yield a null result (the ground is dry); therefore, it probably did not rain.
See also: Autoepistemic logic
Arguments from self-knowing take the form:
In practice these arguments are often unsound and rely on the truth of the supporting premise. For example, the claim that If I had just sat on a wild porcupine then I would know it is probably not fallacious and depends entirely on the truth of the first premise (the ability to know it).