The sense of a proposition is its agreement and disagreement with the possibilities of the existence and non-existence of the atomic facts.
4.21 (1) The simplest proposition, the elementary proposition, asserts the existence of an atomic fact.
4.22 (1) The elementary proposition consists of names. It is a connexion, a concatenation, of names.
4.23 The name occurs in the proposition only in the context of the elementary proposition.
4.24 (3) The names are the simple symbols, I indicate them by single letters ("x", "y", "z").
The elementary proposition I write as function of the names, in the form: "fx", "φ(x,y)", etc.
Or I indicate it by the letters p, q, r.
4.25 If the elementary proposition is true, the atomic fact exists; if it is false the atomic fact does not exist.
4.26 The specification of all true elementary propositions describes the world completely. The world is completely described by the specification of all elementary propositions plus the specification, which of them are true and which false.
4.27 With regard to the existence of n atomic facts there are possibilities.
It is possible for all combinations of atomic facts to exist, and the others not to exist.
4.28 To these combinations correspond the same number of possibilities of the truth - and falsehood - of n elementary propositions.