Another topic that has been brought up many times is the question of analogy. What is its role in scientific reasoning? When is an appeal to it justified, when not? In the thread on "Vacuity", Allen writes:
I would be happy to present a more formal analysis of the relationship between analogy, identity, and validity if any of you are interested. I’ve been working on it for several years, and would be curious to see what your reactions might be.