Difference between 間 and 間に


I have some problems with understanding what is the difference between these
two. According to 初級日本語, 間 refers to certain time frame whereas 間に refers to
certain time frame within that time frame. Is it correct or am I missing
something?




It is very simple:

A 間 B

means;

All the time that A took place B was also happening. (I read my book while it
was raining)

A 間に B

means;

While A took place B happend. The nuance to appreciate is that B is an event
that occurred (started & finished) at some point during the period A took
place. It did not go on all the time. (While it was raining the post was
delivered.)

The nuance is very similar to the difference between まで and までに

A まで B

means;

Until A happens, B will continue, constantly (I was watching television until
father came home)

A までに B

means;

By the time A happens B will have occurred (started and finished, during the
period defined by A まで; it could happend at any point but did not happen
constantly. (I will finish my work by 5 o'clock. ie at some unspecified point
during the period to 5'oclock)

