  Prescriptivists suggest that moral judgments are a species of prescriptive judgement and that moral sentences in the indicative mood are semantically more akin to imperatives than indicatives. One way to think of the idea is that moral terms function as force indicators on analogy with mood.  Early prescriptivists thought that this had radical implications for moral reasoning and argument. Carnap suggested that moral judgments are equivalent to relatively simple imperatives. The statement ‘Killing is evil’ means the same thing as ‘Do not kill.’ On that basis he claimed that there could be no moral knowledge or error (Carnap 1937; 23–24 &amp; 29). 