Logic has its roots in the study of valid argument, but while traditional logicians worked with natural language directly, modern approaches first translate natural arguments into an artificial language. The reason for this step is that some artificial languages now have very well developed inferential systems. There is no doubt that this is a great advantage in general, but for the study of natural reasoning it is a drawback that the original linguistic forms get lost in translation. The program proposed here is aimed at developing a general theory of the natural logic behind human reasoning and human information processing by studying formal logics that operate directly on linguistic representations. Translation of natural language into one of the usual logical languages is in fact unnecessary, we submit, because one level of linguistic representation, that of Logical Form, can meaningfully be identified with the language of an existing and well-understood logic, a restricted form of the theory of types. It is not difficult to devise inference systems for this language, and it is thus possible to study---with the help of all the instruments of modern logic---reasoning systems that are based directly on linguistic representations. We define three subprojects. One will investigate linguistic consequences of this insight and will result in a proof theoretical form of natural language semantics. Another will study the computational logic of different modes of natural reasoning, each based on the systematic search for models that is often taken to be the motor of human inference. A third project will compare the theoretical complexity of model checking tasks for natural language with the cognitive difficulty of these tasks as experienced by human subjects.