I am learning English and I have noticed that "get" is used in most of the passive causative sentences. for example 1) I get shan to write a letter.(Active) 2) I get a letter written(passive) in second sentence we used 'get'. why? and why most of the passive causative sentence contains the word "get" Thanks.
get is a colloquial, conversational way of saying "cause to become".
I got my car washed before the wedding.
I caused my car to be in the state "washed" (i.e. cleaned of dirt). It was dirty before. I caused it to become clean by having someone (or a machine) clean it for me.
My knee has been making popping sounds when I walk.
-- You should get it looked at.
"You should get it looked at" is a colloquial way of saying "You should have it examined".
You should take action that causes a doctor to examine your knee. Once the doctor examines the knee, it is in the state "examined". It has been examined. You have caused your knee to become examined, taking it from the state "unexamined" to the state "examined".
to get someone to do something is an informal way to say: to have someone do something.
- I got Shawn to write a letter. [informal register]
- I had Shawn write a letter. [formal register]
Although you can say: "I had a letter written [by someone]", saying: "I got [or had] someone to write me a letter." is more natural. However, one can imagine the sentence below:
"I had [or got] a suit cleaned for the occasion." [to take a suit to the dry cleaners]
"I had [or got] my hair cut on Friday"/