All right let me ask a question, and and I'm almost done with Copernicus but I want to pause for a moment and ask why should anybody at the time prefer Copernican astronomy to Ptolemaic astronomy. The simple fact of the matter is some people did. Reinhold was sufficiently impressed by it that he did entire tables called the Prutenic tables, that were actually used by the church when they did the Gregorian reform because they were more reliable, more up to date, than the Alfonsine tables were.

Fully recognizing there was a transform. Michael Masslan, Kepler's teacher at Tubingen, was very much a committed Copernican. Various others we will meet in subsequent weeks were Copernicans. Why should they have been so? And the first point is there were no empirical grounds whatsoever for preferring Copernican Astronomy to Ptolemaic Astronomy for the simple reason, that all Copernicus astronomy is, is a mathematical transformation of Ptolemaic that achieves more or less the same level of precision using more recent data for procession and things like that.

So, there's no real empirical grounds you can point to, at the time, just using longitude, observed longitudes and latitudes, to say one of these is to be preferred to the other. The classic argument is, it's simpler, but when we look at it there are no fewer epicycles and I've already made the case equally complicated.

When you read the opening part of De Rev, what Copernicus keeps coming back to is the way the system interlocks, and what he says you can't change anything in it without compensating for those changes elsewhere. By contrast, Ptolemy could do each orbit independently of all the other orbits.

So that interlocking feature looked very attractive to him. There's a huge literature out there in philosophy about why it's rational to prefer Copernican to Ptolemaic even though there was no empirical evidence for it. I'm gonna give you two proposals, the notes go in more detail. I'm gonna give you I think, I'm trying to verbalize.

I'll put it up there. Trying to verbalize the proposal that's come to dominate the philosophic literature. But trying to word it in ways that are free from philosophic jargon. This is a slide that I just added today. That's why some of you may not have it, but I decided it's worth putting in there to make clear that there is an argument here.

So here's my proposal for a principle that I think does indeed describe sociology of science, what scientists actually do all over the place. But I've tried to do it without, and Patrick's the only person in here who realizes how hard I work to try to stay free of philosophy of science jargon, because I wanna describe the actual thing, and then ask whether it fits the philosophic jargon, rather than trying to appropriate the philosophic jargon.

So here's my proposed neutral way. A theoretic proposal put forward as an answer to some one why question, gains support when it provides as corollaries. Answers to why questions regarding other phenomena. When you get a whole lot of answers to why questions for free by giving this answer to one why question.

And the one why question here that's driving this more than any other is why is there retrograde motion? Answer, because the planets are going around the Sun, and the Earth is going around the Sun as well. And retrograde motion is an illusion. And now we start getting a whole bunch of other things popping right out.

We can explain why Ptolemaic astronomy has all those epicycles of the outer planets always pointed toward the mean Sun. Why? Because it's one orbit. It's the Earth Sun orbit. And I can do more of this. How does that fit in to the philosophic literature? Gill Harman introduced, and I've got a typo there, there should be a quote mark at the end, inference to the best total explanation.

He introduced that in the 1960s, I had the pleasure of pointing out to him in fact, actually in a room downstairs at Eaton, that it was in the legal literature from 1910 forward as describing how evidence works in court. The actual phrase inference to the best explanation. It's one way to describe this idea that an answer to one why question gives you for free, answers to a whole bunch of other why questions.

A Popperian would say that gives you all the more opportunities to falsify and that's a good reason for taking it seriously. My guess is most the people at the time who converted to Copernicanism did so because of what I'm trying to voice up here. I may not have voiced it successfully.

But this idea of getting a whole bunch of other answers to why questions, a whole bunch of explanations for other things for free from one. Is definitely place after place in the history of science, reasonably attractive. I'll come right back, now I'm making a point. On the other hand, it's somewhat controversial because there's nothing empirical about that, okay?

Nothing at all empirical about that. Pat?

I was gonna say I like the appeal of the Harmon here and the best explanation, I think that does capture what's going on. But just briefly I think Popper's probably the wrong guy to invoke here.

But he does discuss this and that's one of the attractive things he says.

Because the system interlocks in the way it does, you have all the more opportunities to falsify.

True, but I don't think Popper's being consistent. So, briefly, two reasons If the current system is truly a mathematical transformation of the Ptolemaic system. There shouldn't be any more opportunities to falsify it.

They should have equal opportunity.

That's fair. That's a fair point.

Second, what is really interesting about the view you present here is about how systematic discrepancies are sort of wrangled into place by a theoretical articulation. And that doesn't fit well at all with Popper.

Oh, I understand.

I'll accept that. I'll accept that criticism and I'll remove the Popper from the slide.

Popper said a lot of really interesting things. I just don't think it's good for capturing what

I will accept that. I'm comfortable with that. I mean, exactly how to describe the phenomenon is not obvious.

But the phrase, getting things for free, is the phrase that intuitively I think scientists respond to. And whenever they see it, they wanna pursue it. But it doesn't mean it's true. They're pursuing it because so many things will work out well if it turns out to be true.

And therefore go with it. How's that as a comment? But you don't object to the why question formulation of this.

No I think that's really nice. And inference of the best explanation is, when you put it that way it incorporates these sorts of theoretical concerns. These are questions about pursuit and the effectiveness of the research program, that aren't necessarily just empirical testing for Popper.

If Popper's being consistent, I don't think you can say.

I'll remove the Popper. I was trying to be thorough. But, I agree with you, for the very reason, you gave a good argument. You gave better than a good argument, you gave a definitive argument. If it's a mathematical transformation, it's not gonna make any difference.