陈述句是用来陈述一个事实或表达说话人看法（包括肯定和否定）的句子。通常用降调，句末用句号“.”。
Tom has a new car.
The flower isn’t beautiful.
2. 陈述句否定式的构成
(1) 如果肯定陈述句的谓语部分含有助动词、情态动词或连系动词be，则只需在这些动词后加not即可构成否定式。
He is playing the guitar.（肯定）
He is not playing the guitar.（否定）
We can get there before dark.（肯定）
We can’t get thee before dark.（否定）
(2) 如果陈述句的谓语动词是实义动词，而其中又没有情态动词或助动词时，则需根据人称和时态在该实义动词前加don’t, doesn’t或didn’t。同时把该实义动词变为原形。
He plays the violin well.（肯定）
He doesn’t play the violin well.（否定）
She won the game.（肯定）
She didn’t win the game.（否定）
(3) 如果句子是there be结构或谓语动词是have（有），除了be和have之后加not之外，句中如果有some要变为any。例如：
There is some water in the cup. →There is not any water in the cup.
He has some books. →He has not any books.
(4) 除not以外，否定词no, never, nothing, nobody, few等也可构成否定句。例如：
There is something wrong with his bike. →There is nothing wrong with his bike.
I have seen the film. →I have never seen the film.
二. 祈使句的构成形式及基本用法