Why are formal fallacies considered violations of rules of inference?

Formal fallacies are considered violations of the rules of inference because they represent deductively invalid arguments that fail to adhere to the structural requirements of logical reasoning.123

In formal logic, a valid inference is a rule-governed step where the truth of the premises necessarily guarantees the truth of the conclusion. Because these rules are designed to be truth-preserving, any argument that deviates from these established structures—such as by using an improper process of inference—is inherently fallacious.432

Common examples of these violations include:
* Syllogistic errors: Such as the fallacy of the illicit major or minor premise, which violates specific rules regarding the "distribution" of terms within a syllogism.2
* Propositional errors: Such as denial of the antecedent or affirmation of the consequent, where the logical form of the argument does not support the conclusion drawn from the premises.2

Ultimately, because formal fallacies fail to maintain the necessary connection between premises and conclusion, they are classified as defective argument forms that lack logical necessity.23