text: Fallacies are usually divided into formal and 
  informal fallacies.[38] For formal fallacies, the 
  source of the error is found in the*form*of the 
  argument. For example, denying the antecedent 
  is one type of formal fallacy, as in "if Othello is a 
  bachelor, then he is male; Othello is not a 
  bachelor; therefore Othello is not male".[88] But 
  most fallacies fall into the category of informal 
  fallacies, of which a great variety is discussed in 
  the academic literature. The source of their error 
  is usually found in the*content*or the*context*of 
  the 
  are 
  sometimes categorized as fallacies of ambiguity, 
  fallacies of presumption, or 
  fallacies of 
  the 
  relevance. For 
  ambiguity and vagueness of natural language are 
  responsible for their flaw, as in "feathers are light; what is light cannot be dark; therefore feathers cannot 
  be dark".[90] Fallacies of presumption have a wrong or unjustified premise but may be valid otherwise.[91] 
  In the case of fallacies of relevance, the premises do not support the conclusion because they are not 
  relevant to it.[92] 
  
  argument.[89]  Informal  fallacies 