an argument refers to the situation in which it is used. Based on its context it may be intended to play different roles. One way for an argument to be fallacious is if it fails to perform the role it was supposed to play. The strawman fallacy, for example, involves inaccurately attributing a weak position to one's opponent and then refuting this position. The argument itself may be valid in that the refutation of the opposed position really is successful. The error is found on the level of the context since the opponent does not hold this position. This dependence on a context means that the same argument may be successful in another context: against an opponent who actually holds the strawman position. Natural language and contrast to formal fallacies Formal fallacies are deductively invalid arguments. They are of special interest to the field of formal logic but they can only account for a small number of the known fallacies, for example, for affirming the consequent or denying the antecedent. Many other fallacies used in natural language, e.g. in advertising or in politics, involve informal fallacies. For example, false dilemmas or begging the question are fallacies despite being deductively valid. They are studied by informal logic. Part of the difficulty in analyzing informal fallacies is due to the fact that their structure is not always clearly expressed in natural language. Sometimes certain keywords like "because", "therefore", "since" or "consequently" indicate which parts of the expression constitute the premises and which part the conclusion. But other times this distinction remains implicit and it is not always obvious which parts should be identified as the premises and the conclusions. Many informal arguments include enthymematic premises: premises that are not explicitly stated but tacitly presumed. In some domestic quarrels and political debates, it is not clear from the outset what the two parties are arguing about and which theses they intend to defend. Sometimes the function of the debate is more to clarify these preliminary points than to advance actual arguments. The distinction between formal and informal fallacies is opposed by deductivists, who hold that deductive invalidity is the reason for all fallacies. One way to explain that some fallacies do not seem to be deductively invalid is to hold that they contain various hidden assumptions, as is common for natural language arguments. The idea is that apparent informal fallacies can be turned