English has an inflexible word order which only changes for particular reasons. English is an SVO (subject, verb, object) language; most sentences and finite clauses follow this pattern.
The simplest sentence (apart from single word greetings or exclamations) consists of a subject and a verb.
It's not much of a sentence, and not much of a revelation. But it is a grammatically acceptable sentence. It contains a subject in the form of a one-word noun phrase and a verb in the form of one-word verb phrase. But you are unlikely to see many sentences like these in academic texts. If you do they will probably contain a pronoun referring to something previously mentioned in the text. Something like: "It depends.", "It worked.", "They cry.". Even sentences which only consist of a subject and a verb are usually longer than this, as in the following example.
Now the subject is a two-word noun phrase and the verb is a three-word verb phrase.
In the example above the subject is a noun phrase. All subjects consist of a noun phrase or a nominal clause. This noun phrase contains two words, the article "The" and the headword "baby". The verb is a three-word verb phrase, the lexical verb See the glossary definition "crying" and the primary auxiliaries See the glossary definition "has" and "been". There are some more examples below (click and drag to stop, start and find the sentence you wish to examine):
In each of the examples above both the elements (subject and verb) are obligatory; neither of them can be removed without leaving an ungrammatical sentence. All sentences (except for imperatives) require a subject. All sentences require a verb. If the verb is transitive the sentence requires an object. If the verb is a copula it requires a subject predicative. Noun phrases (especially in academic writing) can be quite long.
There are still only two elements in this sentence; a subject and a verb. The core sentence is "The book has arrived." The word "book" is the headword in this noun phrase. The headword is what you need to identify when you come across long noun phrases. We'll look at noun phrases on the next page. They are important because they are very common and they occupy subject and object positions.