What is the difference? They can read and reply to a PM, but can't create a new one?
If you disable option "Can send PM" they're not able to compose new message or to reply to some of the messages. They can only read it
What happens if I disable can use pm... then they can't read it as well?
If they can't use the PM system they can't receive or send PMs.
is there an option to make it so they can't compose, but can receive and reply?
Composing a PM is part of the reply. What are you wanting to achieve with this setting?
hmmm.... semantics. i meant compose a new PM as opposed to replying to a PM received.
to achieve having a set group not being able to compose a new PM, but still be able to receive and reply to PMs from members with compose a new PM privileges