Informal logic

Informal logic is the form of logic people use in everyday life. It is primarily concerned with making effective arguments, making good decisions, and avoiding logical fallacy. J. Anthony Blair defines "every day argumentation" as "the non-technical arguments of people who are not aware of or self-conscious about discussions of the nature of argument, argumentation or logic". Ralph H. Johnson and J. Anthony Blair define informal logic as "a branch of logic whose task is to develop non-formal standards, criteria, procedures for the analysis, interpretation, evaluation, criticism and construction of argumentation."

While it is extremely important, it is also extremely difficult to boil down to a set of hard and fast rules, because it operates in the uncertain realm of daily life, when many things are unknown to us. For example, juries must seek to use logic to determine whether they believe, "beyond a reasonable doubt," that a person committed a particular crime. However, in most cases, because they cannot actually observe the events surrounding the crime, they cannot know for certain whether or not a crime was committed. To compensate for their uncertainty, they must apply their common sense, their knowledge of human nature, and the evidence presented to them, in order to make a logical decision as to what they think occurred.