I don’t really think of 3 and 4 as very different, there’s definitely a spectrum regarding “plausible” and I think we don’t need to draw the line firmly—it’s OK if over time your “most plausible” failure mode becomes increasingly implausible and the goal is just to make it obviously completely implausible. I think 5 is a further step (doesn’t seem like a different methodology, but a qualitatively further-off stopping point, and the further off you go the more I expect this kind of theoretical research to get replaced by empirical research). I think of it as: after you’ve been trying for a while to come up with a failure story, you can start thinking about why failure stories seem impossible and try to write an argument that there can’t be any failure story...
I don’t really think of 3 and 4 as very different, there’s definitely a spectrum regarding “plausible” and I think we don’t need to draw the line firmly—it’s OK if over time your “most plausible” failure mode becomes increasingly implausible and the goal is just to make it obviously completely implausible. I think 5 is a further step (doesn’t seem like a different methodology, but a qualitatively further-off stopping point, and the further off you go the more I expect this kind of theoretical research to get replaced by empirical research). I think of it as: after you’ve been trying for a while to come up with a failure story, you can start thinking about why failure stories seem impossible and try to write an argument that there can’t be any failure story...
Thanks!