In the philosophy of language and mind, the abstract entities called propositions have a double nature. On one hand, they are units of sense of a fundamental logical type which are expressed by the use of sentences. All propositions represent states of affairs and are true or false depending on how things are in the actual world. On the other hand, propositions are also the contents of conceptual thoughts that we, human beings, have in mind whenever we think, speak or write. As ordinary language philosophers have shown, the primary units of meaning in the use and comprehension of language are speech acts such as assertions, promises and requests which consist of an illocutionary force F with a propositional content P. Moreover, many of our mental states are attitudes like beliefs, intentions and desires which consist of a psychological mode m with a propositional content P. Like illocutionary acts, such attitudes are conceptual thoughts whose contents represent states of affairs.