The results of a laboratory experiment revealed that the participants had generally negative reactions to the use of hedges (e.g. 'may', 'probably', etc.) and pledges (e.g. 'definitely,' 'undoubtedly', etc.) in advertising claims. The use of either type of probability marker reduced claim acceptance and produced more negative cognitive responses relative to when no marker was used. This pattern of results emerged regardless of whether the claim was backed by an inductive argument presenting probabilistic evidence or a deductive argument presenting categorical evidence.