David Deutsch’s idea of hard to vary is also a degree approach: look at the degree/amount of hardness to vary.
I think there’s a way of recasting hard-to-vary as a decisive approach, which is basically the answer ET gave to my first question in this thread.
edit: To be clearer about what I mean, the connection is that if a theory is easy to vary, that means by definition that it contains some unnecessary baggage. On those grounds it can be criticized decisively as not meeting certain (good) goals, such as the goal of having theories without unnecessary baggage.
We should always act on a non-refuted IGC. Why? Better something without a known error than with a known error. That’s what using our knowledge instead of ignoring it means.
I noticed how different this is from the conventional view of errors.
In the conventional view, known errors are completely unavoidable. For example, speaking from the conventional viewpoint: I think of my floor as a rectangle, and that theory has some errors because my floor is not a perfect rectangle. On this view, it wouldn’t make sense to always prefer things without known errors, because if that was your preference then you could never do anything in the real world.
In the CF view, known errors are avoidable. The idea that my floor is a rectangle can only be judged as having an error if it is part of an IGC triplet, and if the goal is something like “I want to put my rectangular desk flush against the wall,” then I know of no errors in that IGC triplet.