"Understanding a sentence means getting hold of its content; and the content of the sentence is in the sentence."

Wittgenstein says that understanding a sentence is not necessarily a mental act. That is, there is no mental act that constitutes "understanding" a sentence. Wittgenstein asserts that understanding, like meaning and believing, fundamentally has to do with the use and context of a sentence, and not with some mental mechanism. Saying you read a sentence by "understanding" it means that you are falsely linking the act of understanding with something outside the sentence itself.