 Not all conventional implicatures are presuppositions in the same way. For example, Jack knows that 51 is prime entails and implicates that 51 is prime. It is false and possibly misleading, but not at all linguistically improper. Other words that trigger conventional implicatures but not presuppositions are start and stop applied to gerunds like cheating (Simons 2001:  432–3).[10]