Tractatus Logico-Philosophicus

Everything that can be thought at all can be thought clearly. Everything that can be put into words can be put clearly.
Propositions can represent the whole of reality, but they cannot represent what they must have in common with reality in order to be able to represent it--logical form.
In order to be able to represent logical form, we should have to station ourselves with propositions somewhere outside logic, that is to say outside the world.
Propositions cannot represent logical form: it is mirrored in them.
What finds its reflection in language, language cannot represent.
What expresses itself in language, we cannot express by means of language...
What can be shown, cannot be said.

Ludwig Wittgenstein, Tractatus Logico-Philosophicus
1961