OK, so I haven't been using the Stack Exchange websites long. However when I have been using them, I've noticed that sometimes you can comment and sometimes you can't.
For example, I just went to comment a question to ask for more details because the question wasn't clear, however the only option other than provide an answer was
Normally there is
Flag | Comment | Edit | Delete or something along those lines.
Why is this? Am I doing something wrong, is it a site bug, or is it done on purpose?