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The Gallileo Affair – a useful primary source of documents

What is it with some philosophical and historical commenters who take sides against Galileo in his 17th century dispute with the Church?

Perhaps because we now have many documents from that period (17th century) – including Galileo’s original writings, official documents from the Inquisition and the church,  and the text of complaints made to the inquisition about Galileo’s beliefs and teachings. This itself can fuel different perspectives.

However, I think another source of this lively debate lies in the preconceived notions and beliefs of the modern protagonists. That, to me, is the only explanation for a trend (a trend – I don’t blame all) among commenters on the history of science that seeks to blame the victim (in this case Galileo) for the affair. To claim that Galileo was scientifically wrong. That the Church was correct to suppress research into a heliocentric model for the solar system. And to threaten imprisonment for anyone holding these opinions. And, inevitably, when there a preconceived beliefs, sources are selected to confirm those beliefs.

We can see one example in Andrew Brown’s blog article Science is the only road to truth? Don’t be absurd  (see my earlier post Debates in the philosophy of science). Here, I want to take issue with his claim that the Church was partly correct in suppressing Galileo’s ideas on heliocentricism:

” Because if there is one thing that has been established in the history of science in the last 50 years, it is that in strictly scientific terms, and going by the evidence available to him and to his contemporaries, Galileo was wrong and Cardinal Bellarmine was right. Heliocentrism was a beautiful theory, and Galileo would have been free to teach it as such — but the observation of stellar parallax, or rather the discovery that none could be observed, should have knocked it on the head “

There are a few points in this which need challenging.

1: Was Galileo “free to teach” heliocentricism?

(As a theory or anything else). I have already commented in  on how arguments about hypotheses and facts were intimately mixed up with theology at the time – the facts being what the Church decided from its interpretation of the “holy” bible. But what in fact had the church told Galileo in 1616? This from the Inquisition Minutes of 25 February 1616:

“His Holiness ordered the Most Illustrious Lord Cardinal Bellarmine to call Galileo before himself and warn him to abandon these opinions; and if he should refuse to obey, the Father Commissary, in the presence of a notary and witnesses, is to issue him an injunction to abstain completely from teaching or defending this doctrine and opinion or from discussing it; and further, if he should not acquiesce, he is to be imprisoned.” [Source The Galileo Affair: A Documentary History by Maurice A. Finocchiaro]

It doesn’t seem that Galileo was free to even hold an opinion, let alone teach it!

2: Was Galileo wrong and Belarmine right?

“In strictly scientific terms, and going by the evidence available to him and to his contemporaries?” Again, questions of right and wrong were confounded at the time because of the overriding theological decisions. But what about the science?

Some commenters place strong reliance on the inability of the original Copernican model to explain some features of planetary movements. This was debated at the time and Galileo’s Reply to Ingoli* (1624) can put these objections into proper perspective:

“. . you criticize the Copernican system by saying, in accordance with Tycho’s authority, that the eccentricities of Mars and Venus are different from what Copernicus assumed, and likewise that Venus’s apogee is not stable, as he believed.

Here it seems to me you want to imitate the man who wanted to tear down his house to the foundations because the chimney made too much smoke, saying that it was uninhabitable and architecturally flawed; and he would have done it had not a friend of his pointed out that it was enough to fix the chimney without tearing down the rest. So I say to you, Mr. Ingoli: given that Copernicus went astray in regard to that eccentricity and apogee, let us revise this, which has nothing to do with the foundations and the essential structure of the whole system.”

“Copernicus was induced to reject the Ptolemaic system, not because he discovered some small fallacy in some particular motion of a planet, but because of an essential and inadmissible incongruity in the structure of all planetary orbits and because of very many great difficulties which are then all removed in his system.”

“So, leave the foundations of the Copernican edifice alone, and repair as you wish the eccentricities of Mars and Venus, and move the latter’s apogee, for these are quantities that have nothing to do with the stability or location of the sun or the earth?” [Source as above]

Of course, there had not been complete proof of a heliocentric system then – nor had there been any such proof of a geocentric system. The authority of the geocentric model rested very strongly on theological justification.

The question of the way that ad hoc adjustments were required to apply a geocentric model is an epistemological one and philosophers of science have discussed this – see 4 below.

3: Did lack of parallax disprove heliocentricism?

Brown is being a bit shifty here as the inability to measure stellar parallax was a matter of sensitivity – it did not prove its non-existence.

One of the beauties of heliocentricism is its ability to produce testable predictions – like stellar parallax. That is the observable location of a distant star against the background stars would differ at different parts of the earth’s orbit around the sun. However, the distance between the earth and the observed stars is so large the parallax is very small and was beyond the sensitivity of the instruments of the time. Copernicus understood this and Galileo used telescopic measurements to conclude that the stars were far more distant from the earth than the proponents of geocentrism argued. (I guess geocentrists would also have to be careful with their argument as they could easily have got into the problem of non-observation of stellar parallax from different locations on the surface of a stationary earth.)

Brown’s flippant claims on stellar parallax were similar to some of Galileo’s opponents of the time. Here’s how Galileo saw them in his reply to Ingoli:

“. . . you should in all honesty have known that Nicolaus Copernicus had spent more years on these very difficult studies than you had spent days on them; so you should have been more careful and not let yourself be lightly persuaded that you could knock down such a man, especially with the sort of weapons you use, which are among the most common and trite objections advanced in this subject; and, though you add something new, this is no more effective than the rest. Thus, did you really think that Nicolaus Copernicus did not grasp the mysteries of the extremely shallow Sacrobosco? That he did not understand parallax?”

“. . . if you had read him with the care required to understand him properly, at least the difficulty of the subject (if nothing else) would have confused your spirit of opposition, so that you would have refrained or completely abstained from taking such a step” [Source as above]

I think this criticism can be addressed to modern critics of Galileo. There seems to be too much cherry picking of arguments to discredit Galileo, by people who do not understand the complexities of the science.

4: The epistemological issues

Almost all the critics of Galileo willfully ignore the huge elephant in the room — the need for indulgence in a huge number of artificial ad hoc adjustments to retain geocentricism.
Philosophers of science often use the geocentric model as an example of bad science because of the indulgence in ad hoc solutions and lack of novel predictions. Alan Chamber, for example, writes in What Is This Thing Called Science?’:

’The Ptolemaic explanation of retrograde motion did not constitute significant support for the program because it was artificially fixed up to fit the observable data by adding epicycles especially designed for the purpose. By contrast, the observable phenomena followed a natural way from the fundamentals of the Copernican theory without any artificial adjustment. The predictions of a theory or progam that count are those that are natural rather than contrived.’

I believe there are important issues in the Galileo affair which relate to the philosophy of science – and especially scientific epistemology.  Many philosophers are well aware of these. However, there are some critics of Galileo with either a philosophical or historical bent who do not seem to appreciate them.

Personally, I don’t think either the history of the Galileo affair, or his contribution to science, can be understood without appreciating these  philosophical and epistemological aspects.

* This was Galileo’s reply to an article by Ingoli directed at him 8 years previously  (1616). While Galileo presented several reasons for the delay he was clearly inhibited by the Inquisition Injunction of 1616 quoted above. He may have been emboldened by the fact of a new, and apparently friendly, Pope coming to office at the time to feel capable of taking up the arguments again.

I mention this because another argument of some apologists for the treatment of Galileo is that his treatment did nothing to hold up the advance of astronomy (see for example An interesting question). I think this delay is just one example showing they are wrong.

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