causative form～させる,when should I use it?
according to my book,the uses are (using the verb 書かせる as example):

a) to have someone write
b) to make someone write (using force)
c) to let someone write (permit or allow)
d) to get someone to write (using trickery,bribery or some other form of inducement)

about "b",we use the "causative passive form",so what's the difference?
about "c" we use 「～てもいいです」they are the same?
"d" also is a bit strange!

I'm really confused...

may you explain it in a simpler way?

Thanks:)

Question

causative form～させる,when should I use it?
according to my book,the uses are (using the verb 書かせる as example):
 
a) to have someone write
b) to make someone write (using force)
c) to let someone write (permit or allow)
d) to get someone to write (using trickery,bribery or some other form of inducement)

about "b",we use the "causative passive form",so what's the difference?
about "c" we use 「～てもいいです」they are the same?
"d" also is a bit strange!

I'm really confused...

may you explain it in a simpler way?

Thanks:)

Answer

"私は彼女に書かせる。"　connotes four types of meaning.
a) I have her write. = I ask her to write.(私は彼女に頼んで書かせる。)
b) I make her write. = I force her to write.(私は彼女を無理やり書かせる。)
c) I let her write. = I allow her to write.(私は彼女の望み通りに書かせる。)
d) I get her to write.= I persuade her to write.(私は彼女に説得して書かせる)

Each type of meaning depends on the context.

Answer

書かせる = 書く + させる
so 書かせる means force to write.

～させる is used when someone force someone to do something.

but sometime it means permission...
If writing is prohibited but now you allow her to write,
then you can say 彼女に書かせる and means "let her write".

In most of case (maybe more than 80%)
～させる means "force someone to do something"
but sometime (guess less than 20%)
～させる means "let someone to do something"

When you have authority to decide what the person do,
you can say ～させる.