Language, Meaning, and Use
The Investigations deals largely with the difficulties of language and meaning. Wittgenstein viewed the tools of language as being fundamentally simple, and he believed that philosophers had obscured this simplicity by misusing language and by asking meaningless questions. He attempted in the Investigations to make things clear: "Der Fliege den Ausweg aus dem Fliegenglas zeigen"—to show the fly the way out of the fly bottle.
A common summary of his argument is that meaning is use—words are not defined by reference to the objects they designate, nor by the mental representations one might associate with them, but by how they are used. For example, this means there is no need to postulate that there is something called good that exists independently of any good deed. This line of thought contrasts with Platonic realism and with Gottlob Frege's notions of sense and reference.
Read more about this topic: Philosophical Investigations