| Cogito ergo sum|
Logic and rhetoric
An informal fallacy (also presumption fallacy, soundness fallacy) is an argument that is formally valid but is unsound because of the lack of truth of one or more of its premises. Informal fallacies are characterised by the fact that although there is a connection between their premises and their conclusion - ie. they have a valid form - their premises are unsupported. All informal fallacies are forms of question-begging. These tend to be more misunderstood and slightly more numerous than formal fallacies.
A few examples of informal fallacies are:
- Ad hoc
- Ad hominem
- Fallacy of ambiguity
- Argument from ignorance
- Post hoc, ergo propter hoc
- Begging the question
- Special pleading
- Weak analogy
- P1: Half of all adult humans can grow beards.
- P2: Sophia is an adult human female.
- C: There is a 50% chance Sophia can grow a beard.
This is not a sound argument because the first premise is irrelevant - an irrelevance which means it is not a valid argument, either: the truth of its premises do not guarantee the truth of its conclusion. As such, it is a formal fallacy.
- P1: The above argument is valid but unsound
- P2: Arguments that are valid but unsound constitute an informal fallacy
- C: The above argument constitutes an informal fallacy
This is not a sound argument because the first premise is not true - however, if it were true, the argument would be sound. As such, it is an informal fallacy.
Usage of the Dixiecrat Fallacy and its Lost Irony
"Next time one of those stupid liberals tells you you’re a racist, you tell him it was the dirty, filthy, stinkin’ ni***r-lovin' democRats what started the KKK. You tell 'em that and it'll blow their minds because they'll realize it's the ni***rs that are the real racists."