I'm just learning desk, so this may be a dumb question.

I have 4 departments, each has a 2-4 forums

I've created a post or two in several forums. Some of the topics I've posted have a space for replies beneath them and others don't.

I can't find where to select to have replies turned on and I can't tell what's different about each context. So - how do I make replies possible or not possible for community users?