Defining a Sentence

Defining a sentence can be a hard thing to do.

Sometimes people say it is 'A complete expression of a single thought', but this can be too vague.

There are sentences that express a single thought but are not complete:

- Nice one, Fred! 

- Horrible Night! 

- Taxi! 

Some sentences are complete and express more than one thought:

- Because it's Sunday, James wants to walk in the park, play on the swings, eat ice cream, and fish in the river.

The formal approach to english grammar looks at the way sentences are constructed - The pattern of the words they contain.

Three things apply to any English sentence:

- It is constructed according to a system of rules known by all the adult mother-tongue speakers of the language. A sentence formed in this way is said to be grammatical. 

- It can stand on its own without feeling incomplete.

- It is the largest construction to which the rules of grammar apply.