The convention that the speaker, in making an assertion, tries to say only what is true, is said to follow from the condition that a speaker must be ready to defend his assertion. After distinguishing theoretical from practical argumentation, practical argumentation is described in terms of the notion 'practical inference', which uses as its cognitive premise an assertion which can be expressed in the form of a 'conditional speech act' (such as warnings, threats, pieces of advice, extortions, negotiations, offers and proposals).