* * * Until now, it was mainly about checking proposals and their meaningfulness. Now we need to dwell on the issue of constructing a scientific theory. Logical positivists treated theory as a logical structure based on sensory data, but rather on the basis of elementary propositions or statements of fact. We have already seen that in the long run, these basic proposals are selected at random. Thus, to construct a theory requires a set of initial proposals and system of rules that allow withdraw of these proposals other proposals, which constitute the upper floors of science. These rules must satisfy one condition: they must ensure the consistency of the system. They must be such as not to allow the display of assumptions conflicting statements. Otherwise, they can be completely arbitrary and is set by agreement. This concept Carnap called "the principle of tolerance." He believed that we possess in every respect complete freedom regarding the form of the language, so that all the postulates and conclusions elimination rules can be arbitrarily selected. Carnap wrote: "In logic, there is no morality. Everyone is free to build its own logic, that is its own form of language of their choice. All that is required from him, if he wants to discuss it, it is clearly set out his method and give syntactical rules instead of philosophical arguments "(32, 52). Thus, here Carnap is of the view conventionalism.