on the other hand, fails to explain the fallacious nature of begging the question since the argument is deductively valid. The Bayesian approach constitutes a special form of the epistemic approach. Bayesianism interprets degrees of belief as subjective probabilities, i.e. as the degree of certainty of the believer that the believed proposition is true. On this view, reasoning based on an argument can be interpreted as a process of changing one's degrees of belief, usually in response to new incoming information. Fallacies are probabilistically weak arguments, i.e. they have a low probability on the Bayesian model. Whether an argument constitutes a fallacy or not depends on the credences of the person evaluating the argument. This means that what constitutes a fallacy for one arguer may be a sound argument for another. This explains why, when trying to persuade someone, one should take the audience's beliefs into account. But it can also make sense of arguments independent of an audience, unlike the dialogical approach. This perspective is well suited for explaining why some slippery slope arguments constitute fallacies but others not. Slippery slope arguments argue against a certain proposal based on the fact that this proposal would bring with it a causal chain of events eventually leading to a bad outcome. But even if every step in this chain is relatively probable, probabilistic calculus may still reveal that the likelihood of all steps occurring together is quite small. In this case, the argument would constitute a fallacy. But slippery slope arguments are rationally justified if the associated probabilities are sufficiently high. Types A great variety of informal fallacies have been discussed in academic literature. There is controversy both concerning whether a given argument really constitutes a fallacy in all of its instances and concerning how the different fallacies should be grouped together into categories. The categorization here follows proposals commonly found in the academic literature in these or similar terms. It distinguishes between fallacies of ambiguity, which have their root in ambiguous or vague language, fallacies of presumption, which involve false or unjustified premises, and fallacies of relevance, in which the premises are not relevant to the conclusion despite appearances otherwise. Other categorizations have been proposed and some fallacies within this categorization could also be grouped in another category. Fallacies of ambiguity The source of the error for fallacies of ambiguity lies in the usage of language. This is due to