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Definition

Circular Reasoning also called circular logic or circulus in probando is an informal logical fallacy meaning arguer uses the same reason as the conclusion. Here is Circular Reasoning example with just rewording same statement.

Everyone must obey the law, because it’s illegal to break it.

Sometimes it forms longer chain: “A is true because B is true; B is true because A is true.” And if chain of propositions longer than that the circularity will be difficult to recognise.

Formal and Informal Fallacies

Logical Fallacies are usually divided into formal and informal. Formal fallacies occuring in Syllogisms are called Syllogistic fallacies.

• A valid argument is the one where if the premises are true, the conclusion must be true. it has a correct formal structure.
• A sound argument is in addition to being a formally correct argument, also contains true premises.

Ideally, the best kind of formal argument is a sound, valid argument. Formal logic checks only argument validity, not soundness, so can not solely be used to determine whether or not an argument is true.

Formal and Informal Fallacies

Logical Fallacies are commonly divided into formal and informal. Formal fallacies occuring in Syllogisms are called Syllogistic fallacies.

• A valid argument has a correct formal structure. A valid argument is one where if the premises are true, the conclusion must be true.
• A sound argument is a formally correct argument that also contains true premises.

Ideally, the best kind of formal argument is a sound, valid argument. Formal logic is not used to determine whether or not an argument is true, they do not take into account the soundness of an argument, but rather its validity.

Definition

Appeal to Authority (argumentum ad verecundiam) logical fallacy and Argument from Authority (argumentum ab auctoritate) are the same form of of discussion argument in which person producing a claim referencing the opinion of an authority as evidence to support an argument. As a fallacy it’s included onto Red Herring Fallacies group.

This can be a fallacy if the referenced person does not have proper authority.

Definition

False Dilemma or False Dichotomy is a formal fallacy based on an “either-or” type of argument. Two choices are presented, when more might exist, and the claim is made that one is false and one is true - or one is acceptable and the other is not. Often, there are other alternatives which haven’t been considered, or both choices might be false or true.