Galileo Attacks Aristotle's Followers

Galileo's Dialogue, Day 2, Part 1

As I wrote in a recent post, I intend to write a post for each of the four days in the Dialogue Comparing the Ptolemaic and Copernican Systems¹, the book that got Galileo in trouble with Rome. Here is the post on Day One: Galileo Dismantles Aristotle's Separation of Earth from the Heavens.

Day Two is the longest day in the Dialogue, for which I will write two posts. This is the first, focussing on a very important exchange between Sagredo, Simplicio and Salviati, used by Galileo to denounce the Peripatetics² (the followers of Aristotle), who refuse to think.

Once the review of Day One is made, the exchange is initiated by Sagredo with the following broadside attack:

One day I was at the home of a very famous doctor in Venice, where many persons came on account of their studies, and others occasionally came out of curiosity to see some anatomical dissection performed by a man who was truly no less learned than he was a careful and expert anatomist. It happened on this day that he was investigating the source and origin of the nerves, about which there exists a notorious controversy between the Galenist³ and Peripatetic doctors. The anatomist showed that the great trunk of nerves, leaving the brain and passing through the nape, extended on down the spine and then branched out through the whole body, and that only a single strand as fine as a thread arrived at the heart. Turning to a gentleman whom he knew to be a Peripatetic philosopher, and on whose account he had been exhibiting and demonstrating everything with unusual care, he asked this man whether he was at last satisfied and convinced that the nerves originated in the brain and not in the heart. The philosopher, after considering for awhile, answered: “You have made me see this matter so plainly and palpably that if Aristotle's text were not contrary to it, stating clearly that the nerves originate in the heart, I should be forced to admit it to be true.”

Galen

What Sagredo is saying is that no matter how much detailed evidence is put right in front of the eyes of the Peripatetics, they refuse to budge, nor to put into question what they believe. Simplicio’s response is hilarious:

Aristotle acquired his great authority only because of the strength of his proofs and the profundity of his arguments. Yet one must understand him, and not merely understand him, but have such thorough familiarity with his books that the most complete idea of them may be formed, in such a manner that every saying of his is always before his mind. He did not write for the common people, nor was he obliged to thread his syllogisms together by the trivial ordinary method; rather, making use of the permuted method, he has sometimes put the proof of a proposition among texts that seem to deal with other things. Therefore one must have a grasp of the whole grand scheme, and be able to combine this passage with that, collecting together one text here and another very distant from it. There is no doubt that whoever has this skill will be able to draw from his books demonstrations of all that can be known; for every single thing is in them.

What Simplicio is saying is truly disturbing: to be able to understand Aristotle is arguing on any given topic, one must know his entire body of work, which is of course an impossibility for the vast majority of people, who do not have the necessary leisure time.

Furthermore, Aristotle supposedly “did not write for the common people.” This is a very important point, because this is exactly what Galileo did, by writing the Dialogue in Italian, the vernacular, as opposed to Latin, the scholarly language of the time. In so doing, Galileo made the debate public, and not private among a limited group of scholars.

But most importantly, if Aristotle did not write specifically about a given topic, the Peripatetics took it upon themselves to combine diverse passages of Aristotle’s to create the arguments they needed. This cut-and-paste approach to “thought” literally can be applied to any topic.

Sagredo reparteed with his usual sarcastic wit:

My dear Simplicio, since having things scattered all over the place does not disgust you, and since you believe by the collection and combination of the various pieces you can draw the juice out of them, then what you and the other brave philosophers will do with Aristotle's texts, I shall do with the verses of Virgil and Ovid, making centos⁴ of them and explaining by means of these all the affairs of men and the secrets of nature. But why do I speak of Virgil, or any other poet? I have a little book, much briefer than Aristotle or Ovid, in which is contained the whole of science, and with very little study one may form from it the most complete ideas. It is the alphabet, and no doubt anyone who can properly join and order this or that vowel and these or those consonants with one another can dig out of it the truest answers to every question, and draw from it instruction in all the arts and sciences.

What Sagredo is saying is that the very idea that any given collection of words contains all of knowledge is by definition ridiculous. Salviati, agreeing with Sagredo, adds an anecdote about the supposed Aristotelian invention of the telescope:

And certain gentlemen still living and active were present when a doctor lecturing in a famous Academy, upon hearing the telescope described but not yet having seen it, said that the invention was taken from Aristotle. Having a text fetched, he found a certain place where the reason is given why stars in the sky can be seen during daytime from the bottom of a very deep well. At this point the doctor said: “Here you have the well, which represents the tube; here the gross vapors, from whence the invention of glass lenses is taken; and finally here is the strengthening of the sight by the rays through a diaphanous medium which is denser and darker.”

This technique is well known, and still used today. Someone makes a new discovery or invents some new device. Along comes someone else, and says, “Oh yeah! So and so over there, back then, worked on this too.” In some cases, this is clearly the case. In others, definitely not. I look forward to examining specific cases of the application of this technique in the future.

In summary, this exchange shows how the Peripatetics were the gatekeepers of the time, claiming that nothing new was being discovered, and that the Standard Model of the time need not be put in question. Sounds like today.

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1. Galileo Galilei. Dialogue concerning the two chief world systems — Ptolemaic and Copernican. Translated by Stillman Drake, foreword by Albert Einstein. University of California Press, 2nd ed., 1967.

2. Peripatetic combines the Greek prefix “peri” (meaning around), and “pateo” (meaning to walk). Hence a peripatetic means someone who walks around. Aristotle had a reputation for walking around the Lyceum while thinking or teaching, so followers of Aristotle have since been called Peripatetics.

3. Galen was a one of the most accomplished of all medical researchers of antiquity.

4. A hotchpotch, a mixture; especially a piece made up of quotations from other authors, or a poem containing individual lines from other poems. From Wiktionary.