I'm looking for the right explanation of the difference between "agree on/about something" and "agree with something."
My guess is that if we agree with something, we second someone's comment, proposal, etc. If we agree on or about something, we focus on the matter we have the same opinion about:
I entirely agree with the comments you made about public transport (I can second them).
The committee members all agree on the need for more information (the focus is on the thing they have the same opinion about - the need for more information).
I feel there is a slight difference between the prepositional phrases, but they don't mean the same thing and are not always interchangeable (although they often can be).
So, how would you explain the difference? Is my guess right? If it is, is there anything to add?