Philosophy 167: Class 4 - Part 16 - Kepler's Three Arguments: From Observations and Reformations of Astronomical Procedures, in Astronomia Nova; From Physical Principles, in Epitome; Comparison Between Calculation and Observation, in Rudolphine Tables.

Smith, George E. (George Edwin), 1938-


  • Synopsis: A review of Kepler's evidential reasoning.

    Opening line: "Kepler gives three types of evidential reasoning. I'm gonna let you read this on your own, you have it. But they're so different from one another, and it enormously complicates the question of why Kepler did not have more influence than he did."

    Duration: 5:36 minutes.

    Segment: Class 4, Part 16.
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Kepler gives three types of evidential reasoning. I'm gonna let you read this on your own, you have it. But they're so different from one another, and it enormously complicates the question of why Kepler did not have more influence than he did. So, in Astronomia Nova, he's working from observations constrained or at least heuristically-informed by some claims about the physics.
But what is driving him is the observations to arrive at the five reforms he does. And ultimately it's the observations that dictate these are the ones, including the ellipse coming out of the diametral distance rule, etc. Then he gets to Epitome of Astronomia, excuse me, Epitome of Copernican Astronomy, and what's he do?
All that reasoning from observations is totally gone. It's nowhere in the book. He tells you, go consult my commentary on Mars, but nowhere does he argue from observation. The only thing he does from observation is values of the elements. The overall generic form of the orbits is entirely derived from a kind of physics.
Of course he knows where he's going so the physics is ad hoc. That's the trouble. But he tried to close the loop, that's a favorite expression of mine, close the loop with the physics, by having it do something beside giving you the area rule in the ellipse, namely solve the move.
And had you, it would have been different. But you know, it's straight forwardly not extracting used, Charles Sanders Peirce's work, he did not adduce his so called laws in The Epitome of Copernican astronomy the way he did in Astronomia Nova. Then in the third work, which by the way there's a couple of things to tell you about that I was worried about the time, it's the first work in which logarithms are presented to be used.
So part of the book teaches you how to use logarithms. He didn't invent them, Napier did. But he saw their virtue and immediately started telling people. He gave log tables and told people how to use them, etc. There are many things about that book that are very impressive.
I probably should. Well, I'm reluctant to pass these around because they're precious books. But the introduction runs 270 pages, and then the tables run about, let's see, another 125 pages. And the tables look like this. And with the tables, you can very quickly do calculations for a given night, a given time.
That's what it's all set up to enable you to do. I pulled this out. It's so beautiful that I'd never Xerox this so I should show it to you since you saw the. Again, I'm not going to pass it around because it's too delicate. And It's Tuft's anyway, not mine.
That's the world from a Rudolphine standpoint. And it's one of the fold-outs from this book. It's an amazing book. But in it, what's he do? He says here, this is how the planets work. Here are the elements. Here are the tables. Go calculate. You're gonna see it agrees with observation.
Okay, that's Lux's very hypothetico deductive. Here's the story. It agrees with observation. If it doesn't agree with observation, you better first figure out whether you've just need to correct an element, not the theory. Which by the way is always a question, you've already heard that question from me.
When you have a discrepancy, what's it telling you? Telling you, you don't have accurate enough elements? Or telling you something's wrong with the theory? That's another evidence problem, that shows up all the time in this. But that's okay. So it's three completely different kinds of evidential reasoning. Historically, just as a matter of historical fact, it looks like the only one that mattered to the world at large was the third one.
That is, they didn't buy his physics, and they didn't go back through the reasoning from observation. But when the Rudolphine Tables were an order and a half magnitude better than anything that had ever gone before, they took notice. And the easy way to describe it, once the Rudolphine Tables were there, nobody was even to be taken seriously unless they could match them.
Okay and people did, but that was the state. But that's what governed it. It was nothing else but that. And in some respects, well I don't wanna say it's the weakest form of evidence here. But it sure is a lot weaker than the evidence in Astronomia Nova. But the very fact that he gives evidence three different ways, it's partly him who created the situation that it's the third way that dominated, cuz the third way is the most accessible.
Anybody can figure out the third way. Does it agree or not? If it agrees then it's gotta be right. That's the kind of reasoning.