I have a vague idea of what you're saying, but I'm still struggling.
If the example of the comet is just that - an example - are there any scientific predictions that are properly conditional? Or, does it follow that all are, in fact, unconditional?
I can see that in the extremities, but don't feel it's necessary to press the point too hard. I've always held that all human systems (whether scientific or not) begin with an assumption, which is akin to an unconditional prediction. But that must be coupled with some common sense for specific problems or it leads to paralysis.
It means, technically, no purely conditional predictions can ever be made. It boils down to the same old "we can't know anything." I think that's one of the accusations leveled against Popper, isn't it? That his philosophy ends up saying science cannot create knowledge.
IMO Popper's ideas are very appealing, and the polemics against him are a bit anal.
But, I don't think I could make anything stand in a debate because I have yet to grasp certain nuances.
Thanks for the help. I'll keep mulling this over.