But you can have an opinion on an objectively verifiable fact. For example, it is raining outside and I say, "In my opinion it is not raining outside." Beyond that I think we would be twisting ourselves up in technicalities because when someone uses 'opinion' the way that this article refers to it, what they are really saying is 'I know' or the state of 'knowing'. Hidden beneath this discussion is the real question: how do we know, what we claim to know? or more concisely: epistemology https://en.wikipedia.org/wiki/Epistemology It is a vast field and definitely worthy of exploration by everyone. Ideally university students would avail themselves of at least one course to learn the basics and begin to learn how to think. This is the most important aspect of higher education after all.