Poisoning the Well is a fallacy which occurs when someone presents unfavorable information about another in order to influence people not to believe or not to take seriously what the person is about to say.
The reason this is fallacious is because negative facts about an individual do not necessarily disprove any arguments that the individual makes. Whether the presented information is true or false, preemptively using it to cause an audience not to take a speaker’s argument seriously is very often fallacious.
Let us consider a few examples to better understand this fallacy:
Example 1: Jack says, “Before we welcome Michael onto the show to discuss the proposed Senate bill, let us take a moment and remember that this individual is a convicted felon and perjurer.”
Notice how Jack is using the fact that Michael is a convicted felon and perjurer to bias us against anything he would say. This is fallacious because any argument Michael makes needs to be evaluated based on the evidence for or against it. While it is not good that Michael committed the crimes he did, it should have no bearing on the argument he will be making.
In some cases, negative information does have bearing on a person’s credibility. However, that depends on the argument being made. If Michael was arguing that he is a trustworthy man who would never lie, the fact that he was a perjurer and felon would naturally make us think otherwise. On the other hand, if Michael was arguing for the earth being round, his crimes have no bearing on that argument. Presenting the negative information before the individual presents their argument is still unacceptable because it is a mistake to dismiss someone’s argument before they even have an opportunity to let you know what it is and to present it.
Example 2: Rose says, “In a moment, Todd is going to present his argument in favor of position X. However, let us remember that all arguments for position X have been proven false.”
Rose’s statement implies that because all previous arguments in favor of position X have been defeated, no strong argument can be given for position X. This is a fallacious statement because even if it were true that all the arguments in support of position X have been proven false, that does not mean one is justified in automatically rejecting what Todd has to say. If Todd is going to present a new argument in favor of position X, his argument will have to be tested on the basis of the evidence for and against it. The fact that all previous arguments for position X have failed does not automatically negate Todd’s argument. This is easily seen if one imagines that Todd is living during the time of Plato and Aristotle and is arguing for the heliocentric model as opposed to the geocentric model. Just because all previous arguments for heliocentrism have been defeated does not mean Todd can not give a good argument in favor of it.
In conclusion, attempting to bias an audience against what a speaker is about to say is a logical fallacy. When someone is going to present an argument, it is important to allow them to make their argument before you judge it.