I think that I have finally created a definition of Critical Thinking that seems to work in the context of a class blog discussion. It's certainly different from the definitions that I surveyed in other contexts.
Critical Thinking in a class blog discussion demonstrates an understanding of the text, the ability to draw conclusions or ask good questions about it, and the ability to engage the ideas of other students or to make connections to previous knowledge, other texts, contexts, or ideas.
I've actually thought about this definition so much that I'm having serious internal debates about the placement of the words "and" and "or." I can't find a combination that I'm perfectly happy with. I think the second "or" should be an "and" . . . maybe. I also think this a sign that I have thought about this too much and need fresh insight.