Full Idea
Some argue that metaphysical accessibility is intransitive. The individuals involved mustn't be too different from the actual world. A world in which I am a frog isn't metaphysically possible. Perhaps the logic is modal system B or T.
Gist of Idea
Maybe metaphysical accessibility is intransitive, if a world in which I am a frog is impossible
Source
Theodore Sider (Logic for Philosophy [2010], 6.3.1)
Book Reference
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.142
A Reaction
This sounds rather plausible and attractive to me. We don't want to say that I am necessarily the way I actually am, though, so we need criteria. Essence!