Formal fallacies are errors in reasoning that occur due to a flaw in the logical structure of an argument. These fallacies can make an argument invalid, even if the premises are true. Common examples include the affirming the consequent and denying the antecedent, which misinterpret the relationships between premises and conclusions. Unlike informal fallacies, which often involve issues with content or context, formal fallacies focus solely on the form of the argument. Recognizing these fallacies is essential for critical thinking and effective reasoning, as they can undermine the validity of conclusions drawn from flawed premises.