In the Preface of Tractatus Logico-Philosophicus, Wittgenstein writes that

the aim of the book is to draw a limit to thought, or rather – not to thought, but to the expression of thoughts: for in order to be able to draw a limit to thought, we should have to find both sides of the limit thinkable.

(TLP, 3, see TLP 4.114) According to the traditional interpretation of the book, this task is accomplished by presenting a theory of linguistic sense, known as the picture theory of meaning. According to this theory, every meaningful proposition is a picture of a possible state of affairs. The picturing of states of affairs requires, in turn, referential relations between the elements of the picture and the pictured and the ability of those elements to be connected with one another as the elements of the pictured state of affairs are connected (TLP 2.1514, 2.151). This structural isomorphism between the picture and the pictured is made possible by logical form shared by language and the world (TLP 2.033, 2.17). When a proposition is analyzed into its simple elements, that is, names, each name, as a constituent of the proposition, has a logical form that corresponds to the form of the object to which it refers in the state of affairs. The logical forms of objects thus ground the logical form of states of affairs as well as of the propositions depicting them. Hence, Wittgenstein writes, “Logic pervades the world: the limits of the world are also its limits” (TLP 5.61).