I am struggling to understand Could and Not Necessarily
I am trying to understand possibility indicators as described in Chapter 3. But the logic doesn't feel intuitive to me, or adjacent to how I'd use the words in real life. I've constructed my own example, but can someone help correct my logic if it's incorrect?
What I've gathered is that if you have a premise set and a conclusion, the conclusion is valid if in every universe you construct, the premises are true and the conclusion is true. Here's an example premise + conclusion I made:
>Psycholinguists, at Harvard University, an institution regarded for its great prestige and rigor in language studies, found that people are far more likely to understand the phrase 'not necessarily false' less intuitively than 'could be true' despite their equivalence. It's possible most readers of this will be more confused about the former than the latter of those two phrases themselves.
At first glance, I thought the conclusion was valid (and so does ChatGPT). But then I thought what if those reading this are logicians, or LSAT experts, or linguists themselves, or some other self selected group of people. Then it'd be certain that most of them aren't confused by not necessarily false. So in that case would I conclude the conclusion isn't valid since there's a reasonable universe where the premises are true but the conclusion about possibility is not? Am I thinking about this the correct way?
Sorry for the long text. Thank you!