‘Ex falso quodlibet’ is a Latin phrase which literally means ‘from a falsehood, anything follows’. Philosophers use this term to refer to a principle of classical logic, which says that from a contradiction, anything follows. (Logic is the science of inference. A logical system tells us what we are allowed to infer from what, and classical logic is one such system.) The principle is thus also known as ‘explosion’, since it allows us to infer absolutely anything as a conclusion when an argument has a contradiction as its premise.
Some find the principle intuitive: after all, if the world was such that a contradiction could be true, surely anything could be the case! However, not everyone agrees that the principle is a good one, since many believe that a conclusion should be relevant to its conclusion, and Ex falso quodlibet undermines this. For example, according to classical logic, we can infer that snow is purple, that 2+2=5, and that the Earth is a unicorn’s tear from the supposition that drinking tea is good for the soul and is also not good for the soul, and that seems ludicrous. Whether tea-drinking is good for the soul seems to have absolutely nothing to do with whether the Earth is a unicorn’s tear, or that 2+2=5! | |||