Fallacies

Fallacies

Formal fallacies

Formal fallacies are arguments invalid but often accepted because of its similarity with valid forms of reasoning or inference. It gives an error that goes undetected. For example, based on two premises as "If it rains, I take the umbrella" and "There is the case it rains," I can conclude with formal validity "I take the umbrella." However, the two premises: "If it rains, grab an umbrella" and "I take the umbrella," I cannot conclude with formal validity "Rain": if I took the umbrella was because I had to fix it. This is an example of the fallacy known as formal affirmation of the consequent. The ecological fallacy arises when inferences are made about the characteristics of individuals in a population based on analyses using aggregate statistics of those same individuals. The general usage of the term applies to inferences made about individuals that are based solely on the group characteristics of that population (Kuther, 2003, pp. 343-358).

Such would be the case with stereotyping or geographical profiling, where individuals are characterized by the general traits of the area in which they live. In a more specific manner, the ecological fallacy occurs when an ecological correlation between variables based on statistical constants such as group rates or means is assumed to characterize individual members of that population. William Robinson first demonstrated that statistical correlations of variables aggregated by group or geographic area can differ markedly from correlations based on individual-level variables of that same population.

1- Affirmation of the consequent

Reasoning based on a conditional (if p then q) and giving or stating the second or subsequent, people conclude p, which is the first or the antecedent. Example: "If it rains, grab an umbrella, I take the umbrella. Then it rains (Tversky, 1974, pp.1124-1131)."

2- Denial of the antecedent

Reasoning ...