Poisoning the well
Poisoning the well (or attempting to poison the well) is a fallacy where irrelevant adverse information about a target is preemptively presented to an audience, with the intention of discrediting or ridiculing everything that the target person is about to say. Poisoning the well can be a special case of argumentum ad hominem, and the term was first used with this sense by John Henry Newman in his work Apologia Pro Vita Sua (1864). The origin of the term lies in well poisoning, an ancient wartime practice of pouring poison into sources of fresh water before an invading army, to diminish the attacking army's strength.
If Adam tells Bob, "Chris is a fascist so do not listen to him", then Adam has committed the fallacy of poisoning the well, as fascism is seen as a "bad" ideology in modern Western civilization; if Bob takes Adam's advice then he is a victim of the fallacy of poisoning the well. Assuming that Chris is not merely going to tell Bob that he is not a fascist then there is a fallacy because it is irrelevant to the cogency of Chris' argument(s) whether he is or is not a fascist. It is possible to be a fascist and also to have cogent arguments on some arbitrary matter, e.g. Chris may wish to persuade Bob that the Earth is not flat; being a fascist does not preclude the possibility of having a cogent argument that the Earth is not flat.
A poisoned-well "argument" has the following form:
- 1. Unfavorable information (be it true or false) about person A is presented by another. (e.g. "Before you listen to my opponent, may I remind you that he has been in jail")
- 2. Therefore, the claims made by person A will be false. 
A subcategory of this form is the false dilemma; an unfavorable attribute to any future opponents, in an attempt to discourage debate. (For example, "That's my stance on funding the public education system, and anyone who disagrees with me hates children.") Any person who steps forward to dispute the claim will then risk applying the tag to him or herself in the process.
A poisoned-well "argument" can also be in this form:
- 1. Unfavorable definitions (be it true or false) which prevent disagreement (or enforce affirmative position)
- 2. Any claims without first agreeing with above definitions are automatically dismissed.
- Ad hominem
- Appeal to ridicule
- Black propaganda
- Framing (social sciences)
- Fruit of the poisonous tree
- Guilt by association
- Scorched earth
- Evil reptilian kitten-eater from another planet