 Presuppositions differ from propositions in one fundamental respect: propositions have truth-values. They are asserted as either true or false. Presuppositions, on the other hand lack truth values; they are neither true nor false. This is because they do not fulfil their role (that of giving rise to questions) in virtue of being true or false. Just as the validity of an inference does not depend on whether the premises from which the inference is drawn are true or false, so the “logical efficacy” (EM 1998: 27) of a presupposition, i.e., its power to give rise to a question, does not depend on the presupposition being either true or false, or even on being believed to be true or false. This consideration, Collingwood says,