When a fallacy occurs, an arguments has been rendered defective by an error in reasoning. The error can be identified in one of at least five ways as follows: It would arise from giving wrong grounds. It could be a wrong way of connecting the grounds to the claim. It could be a wrong way to understanding the use of words in an argument. It could be a wrong way of construing the facts of the arguments. It could be identified as a wrongly structured argument. In a fallacy, therefore, given the premise or premises, no conclusion follows or can be inferred, or the conclusion advanced is not that which really follows or the alleged conclusion follows only because the premises contain an illegitimate assumption.
A reasoned who suggests that a claim is true, or false, merely because he or she strongly hopes it is, is using the fallacy of “wishful thinking”. Wishing something is true is not a relevant reason for claiming that it is actually true. An example of a fallacy of wishful thinking goes thus: “There’s got to be an error here in the history book. It says Thomas Jefferson had slaves. I don’t believe it. He was our best President and a good President would never do such a thing”. That would be awful.
Hopes, desires, and aversions can also lead us astray logically. The fallacy known as wishful thinking happens when we accept or argue acceptance (or rejection) of a claim simply because it would be pleasant (or unpleasant) if it were true. A smoker for example, may refuse to acknowledge the wealth hazards of smoking. We’ve had students who are in denial about the consequences of cutting classes. The wishful thinking fallacy also underlies much of the empty rhetoric of “positive thinking” –rhetoric that claims “you are what you want to be” and other such slogans. Wishful thinking can be a powerful influence and can sometimes defeat all but our most committed efforts to do the rational thing.
Our personal interests and biases affect our perceptions and the judgements we base on them. We overlook many of the mean and selfish actions of the people we like or love –and when we are infatuated with someone, everything that person does seems wonderful. By contrast, people we detest can hardly do anything that we don’t perceive as mean and selfish. If we desperately wish for evidence for that success than is actually present. On the other hand, if we wish for a project to fail, we are apt to exaggerate flaws that are not there at all. If a job, chore, or decision, we are more likely to focus on whatever positive consequences it might have.