Thus, from a linguistic point of view, we could say that the word «non-existence» («nihil») or the phrase «there is no such thing as non-existence» («gaunenlos siegen nicht») are meaningless expressions.

It is important to note that the Tractatus does not state that the only sentence that matters is the true sentence. It is possible to define sentences in languages in which it is impossible to say anything about the meaning of a sentence so that they can be used to define what is real, and Wittgenstein even argued that sentences in such languages make sense.

The term «theory» is used by Wittgenstein in a completely different way. For him, theory is a formal system (in the sense of the «language of theory») in which a number of statements about the real are attributed to objects and properties in the model of the world.

It is not immediately obvious that it is possible to define a «model of the world» in the sense in which Wittgenstein used the term, but he did. The «model of the world» that Wittgenstein defines in this context is not a physical model, but a logical model. (This can be viewed as the same as how some prefer to think of it as a model of a given mathematical theory.)

A theory in theoretical language is a set of statements about the real that can be used to determine the reality of something.

A good example of a theory is Einstein’s special theory of relativity, which, thanks to the use of a mathematical formal language, is perfectly suited to describe what happens to an observer in a special system of relativistic physics.

If the model of the world doesn’t really explain everything about the world, then it may not be a very good model after all.

Indeed, some say that the logical positivist system can actually explain more about the world than any theory it discusses. But if the system of logical positivism is not a very good model of the world, it can still be used to determine whether something is real.

To use Wittgenstein’s terminology, the distinction between the real and the unreal for Wittgenstein is «visual.»

For logical positivists, the world is «non-visual».

Wittgenstein, however, does not regard the world as" non-visual, "and even if it were, it would not be a problem: it is entirely possible to describe the world in visual language. In any case, the world is a visual object, even if the universe it is in is not.

The central theme of Wittgenstein’s later philosophy is his view that language cannot distinguish between the real and the unreal, that the world is an understandable world, and that the meaning of a statement can be determined using this statement.

Some critics have argued that these views do not «challenge» the traditional position that the world is understandable, but that they do challenge the old position that language cannot be used to distinguish the real from the unreal.

According to Alfred Jules Ayer, metaphysicians claim to have «a knowledge of reality that [transcends] the phenomenal world.» Ayer, a member of the Vienna Circle and a well-known English logical positivist, argued that it was impossible to make any statements about the world outside of direct sensory perception. If an empirical statement such as «The earth revolves around the sun,» Ayer argues, is a statement about the world outside the realm of sense perception, then that too cannot be explained.

The Philosopher John F. Bennett formulated the «ontological anti-realistic" view of truth and truthfulness, which defies the «spirit of ontological relativism that permeates much of metaphysics» and against what Ayer, George Dyson and many other philosophers opposed to competing concepts of metaphysics in the 20- m and 21st centuries.