for fear v.s in case

for fear that =possibility; chance 唯恐, 害怕

for fear of/that/lest + may/might/should


there is no fear of that happening to forestall or avoid


for fear of   so as not to 
She would not go swimming for fear of catching a cold.

in fear of  in a state of being afraid of 
He lived in fear of his mother.


Shut the door for fear that it may rain.
He wrote the name down for fear that he might forget it
She is working hard for fear that she should lag behind others.


in case  假使, 如果, 萬一

in case ＋ of ＋ 名词／子句  *一般時態或假設should do

In case of rain they can't go.
Take a hat with you in case the sun is very hot.
Take an umbrella with you in case it should rain.