The diagram S NP+VP means that a sentence can be rewritten as a noun phrase plus a verb phrase. This is a one of the phrase structure rules by Noam Chomsky (1957). The purpose of these syntactic rules is to break down sentences into their constituent parts (syntactic categories) including both lexical categories and phrasal categories.
S NP+VP reads as follows: A S(sentence) consists of an NP (noun phrase) followed by a VP (verbal phrase). By following these rules, you are able to construct multiple English sentences yet, as the theory is merely based on the structure and does not consider other factors, it is highly possible to make constructions that are semantically old. For instance, the well-known sentence "colorless green ideas sleep furiously".
This sentence was constructed by Chomsky to show that phrase structure rules are capable of generating syntactically correct but semantically incorrect sentences.
