People are very well able to distinguish them -- we are doing so right here.
Are we? We're discussing the distinction, sure, but is each of us distinguishing the other's statements about implicature from the other's implications about implicature? Did I say everything you think I said? Did you say everything I think you said?
If I read this thread, then attempt to write down a list of significant statements you made from memory, and then compare that list to your actual text; will it contain things you did not say? Will it also contain things that I thought followed from what you said, but that you neither said nor meant?
My understanding of the original quote is that it will. I found that surprising, enlightening, and scary.
We're discussing the distinction, sure, but is each of us distinguishing the other's statements about implicature from the other's implications about implicature?
No, because we do not need to. We are responding to what we perceive the others' meanings to be, regardless of how explicitly they were expressed. Only if we are are uncertain of an implication, or if one person perceives an implication that another did not intend, do we need to raise the issue.
...If I read this thread, then attempt to write down a list of significant statements you made from me
I'm reading Thinking, Fast and Slow. In appendix B I came across the following comment. Emphasis mine:
My first thought on seeing this is: holy crap, this explains why people insist on seeing relevance claims in my statements that I didn't put there. If the brain doesn't distinguish statement from implicature, and my conversational partner believes that A implies B when I don't, then of course I'm going to be continually running into situations where people model me as saying and believing B when I actually only said A. At a minimum this will happen any time I discuss any question of seemingly-morally-relevant fact with someone who hasn't trained themselves to make the is-ought distinction. Which is most people.
The next thought my brain jumped to: This process might explain the failure to make the is-ought distinction in the first place. That seems like much more of a leap, though. I looked up the Clark and Clark cite. Unfortunately it's a fairly long book that I'm not entirely sure I want to wade through. Has anyone else read it? Can someone offer more details about exactly what findings Kahneman is referencing?