The aim of the book is to set a limit to thought, or rather - not to thought, but to the expression of thoughts: for in order to be able to set a limit to thought, we should have to find both sides of the limit thinkable (i.e. we should have to be able to think what cannot be thought). It will therefore only be in language that the limit can be set, and what lies on the other side of the limit will simply be nonsense.