Thank you, Professor. That definitely helped.
I may have answered my second question as I was typing it up. I was a little confused about real supposition in abstract terms. McCall lists “Justice is a virtue” as an example.
Maybe it’s better just to ask for some further reading on the subject of supposition? McCall lists Jacques Maritain’s ‘Introduction to Logic’ as a great resource, but I’m not sure if this covers informal logic. Or perhaps one of the books on the bibliography page covers the topic of supposition?