and，or，but這三個連詞分別稱作等立連詞、選擇連詞、轉折連詞，可以用來連接任何同類的詞、短語和句子。下面先以and為例：
1、連接並列的各種詞類，如：
Two and two makes four.二加二得四.（數詞）
Read slowly and loudly.讀得既要慢些又要大點聲音。（副詞）
She is beautiful and cute.她又漂亮又可愛。（形容詞）
He went there to and fro several times.他來來回回去了那裏好幾次。（小品副詞）
My father and mother are both workers.我的父母都是工人。
Try and shoot the bird.開槍打那只鳥試試。（用在go, come, try, write或see與其他動詞中間表示目的）
We talked and talked.我們說呀,說呀,說個沒完沒了。（用在兩個意思相同的動詞之間反復發生的行為）
We ate and drank to our full content.我們盡情地連吃帶喝飽餐了壹頓。（連接其他動詞表示同時或緊接著進行的行為）
2、連接各種並列成分，如：
He is at home and does his homework at the desk.她在家伏案做作業。（並列謂語）
He went out of the door and into the dark.她出了門走進黑暗之中。（並列狀語，介詞短語）
The boy at home and in bed caught cold.呆在家躺在床上的男孩感冒了。（並列後置定語）
3、連接並列句。如：
I did not answer, and he, too, kept silent.我沒有回答, (而)他也不作聲。
Go at once and you will see her.馬上去,那麽妳就會見到她了。
The cure for bad teaching is good teachers, and good teachers cost money.解決教學質量差的辦法就是請好的教師，但請好的教師是需要花錢的。
All through yesterday crowds have been arriving and by midnight thousands of people packed the square.昨天陸續有大批人到來，午夜時有幾千人聚集在廣場上。
You could only really tell the effects of the disease in the long term, and five years wasn't long enough.真的，這種病只能在很久以後才能看出它的影響，而5年的時間還不夠長。
同理，or 和 but 也是如此。
John or you are in Class Two.約翰或者妳在二班。（名詞）
two or three miles兩三裏(距離)（數詞）
late last night or rather early this morning昨晚深夜,或者更確切地說,今天壹早。（形容詞）
He cannot read or write.他既不會讀也不會寫。（動詞）
Make haste, or (else) you'll be late.快點,要不然就來不及了。（句子）
No one but she saw the prowler.除了她以外沒有壹個人看見那個行竊者。（代詞）
It never rains but it pours.光打雷不下雨。（句子）
There is no doubt but right will prevail.毫無否定疑問，正義將取得勝利。（句子）
There never is a tax law presented but someone will oppose it.現行的稅法沒有壹條是沒人反對的。（句子）