Something is true because it has not yet been proved false
Argument from ignorance.
One might claim that if there is some evidence for a certain view, X, while no evidence exists for the opposing view, ¬X, this makes X more likely for the time being.
A good example of this would be an argument made by the English physician William Harvey, discoverer of the circulation of blood in human beings. Harvey claimed that his findings should be considered probable until somebody manages to prove them wrong[1].
Non-Fallacious Ad Ignorantiam Arguments. Retrieved June 13, 2024. ↩︎
Whilst argument from ignorance is a logical error, there are situations when it is practical to assume that something is false until proven otherwise or vice-versa. For instance, in the legal system it is assumed that every person accused of any crime is considered innocent until proven guilty. A person might get acquitted during the trial, yet later found guilty of the crime[1]. However, this is a trade-off that we as a society make in order not to send an innocent person to prison.
In science we often also assume the argument from ignorance for pragmatic reasons. For instance, take the science of radioactive decay. There is no evidence that the decay rate of U238 was different in the past than it is in the present. If we conclude that the rate of decay was no different in the past, the science of radioactive decay and its uses becomes possible[1:1].
Argumentum ad Ignorantiam: The Argument from Ignorance. Retrieved June 13, 2024. ↩︎ ↩︎
The argument from ignorance makes a logical error by claiming that a lack of evidence for some proposition proves the opposite [1]. Formally:
Statement p is unproved
∴ ¬p is true
or
Statement ¬p is unproved
∴ p is true
For example, somebody might fallaciously claim that God does not exist, because nobody has seen it.
Here is another example of a fallacious claim made by Weston Walch, a writer on railroad practices:
It cannot be proved that government ownership of railroads has succeeded in other countries. Therefore, government ownership of the railroads should not be adopted in this country[2].
Just because we have no evidence of government ownership working in other countries does not logically imply that it does not work in general[1:1].
Argumentum ad Ignorantiam: The Argument from Ignorance. Retrieved June 13, 2024. ↩︎ ↩︎
Walch, J. W. (1939). Complete Handbook on Government Ownership of Railroads. Platform News. Retrieved from https://philosophy.lander.edu/logic/ignorance.html. ↩︎