How Logic Works – Informal Logic

appeal to authority - doctors and camels

While Formal fallacies are a matter of invalid form. Informal fallacies are a matter of unclear expression.

An informal fallacy involves such things as: the misuse of language — words or grammar, misstatements of fact or opinion, misconceptions due to underlying presuppositions, or plain old made up bullshit.

An easy example of an informal fallacy is to mistake the word “informal” (in informal fallacy) to mean inferior, casual or otherwise less important. In reality, it only means that our focus is not on the form of the argument, but on the meaning of the argument.

Some classic examples of inductive arguments:

Informal logic


Logic teaches you how to argue.
Arguing leads to truth.
Teaching people logic is productive.

In the above example, we are using the definition of argue as follows:

A course of reasoning aimed at demonstrating a truth or falsehood; the methodical process of logical reasoning

This meaning of arguing is in-line with the use of logic and is an accurate use of the word argue.


Logic teaches you how to argue.
Arguing gets us nowhere.
Teaching people logic is unproductive.


Although there is a colloqual meaning of argue referring to a ready disposition to fight, this is a misrepresentation of the word, one used to distract from the true use of logic, in this case it is used to place logic in an undeserved negative light.

You have likely heard or seen this common fallacy, which follows the same abuse of ambiguity, before:

Evolution is just a theory

In short, informal fallacies are invalid reasoning — arguments where the premises, even if factually correct, are misused in order to come to a poorly reasoned conclusion.

As with formal logic, while the conclusions may be true, their truth is not a result of the premises presented.

Informal fallacies, having many different categories, are the most difficult to detect and are where this site focuses. Check them out

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