Logical fallacies are errors of reason that can occur in inductive reasoning. Since inductive reasoning moves from the particular to the general, it is important to determine how much and what kind of evidence you need to make a valid argument. Failure to have proper evidence is linked to several kinds of logical fallacies.
Since logic is one of the main techniques used in persuasion, being able to identify and discount logical fallacies in others' arguments and avoid making them in one's own arguments are both important. One of the things that can undermine logic is basing an argument on insufficient evidence. There are several errors that one can make related to insufficient evidence as one chooses evidence to bolster an argument, and the following fallacies of insufficient evidence occur so frequently that they are named.
Hasty Generalization. A hasty generalization bases a conclusion on too little evidence. An example is: This winter was colder than last winter: the climate must be getting colder. This is a logical fallacy of insufficient evidence because more evidence than a change for one year is needed to establish a climatic trend.
Fallacy of Exclusion. Leaving out evidence that would lead to a different conclusion is called the fallacy of exclusion. An example is: In the presidential elections of 2000 and 2005, Florida went to Bush, so it must be a Republican state. In fact, the evidence from 1996, which I purposely excluded from the sentence above, shows that Florida went to Clinton in that election, making this, too, a fallacy of insufficient evidence. By choosing to begin with the data from 2000, I was able to exclude evidence that contradicted the conclusion I wished to draw for the sake of this exercise.
Fallacy of Oversimplification. In this fallacy, some aspects of an issue -- generally more subtle ones -- and their ramifications are not explored. An example is: The question of funding medical research comes down to this: do we want to heal the sick and help the injured to recover -- or not? This argument ignores questions of funding sources, differing states of research in different areas of health care, an so on, so it falls into the category of insufficient evidence. By avoiding reference to any complexities, including the possibility that some issues may never have a successful resolution, this argument makes the choice seem to be solely about good will towards the less fortunate.
