A fallacy is reasoning that is logically incorrect, undermines the logical validity of an argument, or is recognized as unsound. All forms of human communication can contain fallacies. Because of their variety, fallacies are challenging to classify. They can be classified by their structure (formal fallacies) or content (informal fallacies). Informal fallacies, the larger group, may then be subdivided into categories such as improper presumption, faulty generalization, error in assigning causation, and relevance, among others.