well, maybe sometimes it can be a hard line to mark.. but i think normally its pretty clear cut.. if you are presenting a fact then you will be referring to something external which is qualitative or quantitative.. it could indeed change, and there are many different facts you can choose from.. but facts are facts.. observable things that are external to us.. then opinions are personal things we may base on facts (hopefully) but no always.. opinions are like you choose which facts to look at, or dont even bother at all :)