Galileo Galilei Supports Atomism, Part I

Il Saggiatore (The Assayer¹) is a polemical text that Galileo Galilei wrote in response to Orazio Grassi (using the pseudonym Sarsi), on the nature of the comets that appeared in 1618. With respect to the comets, Galileo was in error, arguing that they were sublunar. Notwithstanding this error, this text is crucial, as it is therein that he writes extensively about the methodology of science.

It is in the The Assayer that Galileo famously wrote:

Philosophy is written in this grand book — I mean the universe — which stands continually open to our gaze, but it cannot be understood unless one first learns to comprehend the language and interpret the characters in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometrical figures, without which it is humanly impossible to understand a single word of it; without these, one is wandering about in a dark labyrinth. [pp.183-184]

This passage is explicitly cited in Alexandre Koyré’s argumentation that Galileo was a Platonist:

One sees that for the scientific and philosophical consciousness of the time … the opposition, or rather the dividing line, between the Aristotelian and the Platonist is perfectly clear. If you claim for mathematics a superior status, if more than that you attribute to it a real value and a commanding position in Physics, you are a Platonist. [p.421]²

But The Assayer is also important in that Galileo expresses his support for the atomic model of nature, and that the qualities that we perceive of any object are not inherent to the object, but, rather, come from our own senses. Galileo, in arguing that “Motion is the cause of heat,” prepares us with the following:

Therefore I say that upon conceiving of a material or corporeal substance, I immediately feel the need to conceive simultaneously that it is bounded and has this or that shape; that it is in this place or that at any given time; that it moves or stays still; that it does or does not touch another body; and that it is one, few, or many. I cannot separate it from these conditions by any stretch of my imagination. But that it must be white or red, bitter or sweet, noisy or silent, of sweet or foul odor, my mind feels no compulsion to understand as necessary accompaniments. Indeed, without the senses to guide us, reason or imagination alone would perhaps never arrive at such qualities. For that reason I think that tastes, odors, colors, and so forth are no more than mere names so far as pertains to the subject wherein they reside, and that they have their habitation only in the sensorium. Thus, if the living creature (l’animale) were removed, all these qualities would be removed and annihilated. Yet since we have imposed upon them particular names which differ from the names of those other previous real attributes, we wish to believe that they should also be truly and really different from the latter. [p.309, emphasis mine]

After giving a number of examples illustrating this idea, Galileo concludes as follows:

I do not believe that for exciting in us tastes, odors, and sounds there are required in external bodies anything but sizes, shapes, numbers, and slow or fast movements; and I think that if ears, tongues, and noses were taken away, shapes and numbers and motions would remain but not odors or tastes or sounds. These, I believe, are nothing but names, apart from the living animal — just as tickling and titillation are nothing but names when armpits and the skin around the nose are absent. [p.311, emphasis mine]

These few pages are crucial, as is explained by Paolo Galluzzi, director of the Museo Galileo in Florence, in a presentation given to the Festival filosofia in Carpi, Italy, in 2011.

Below is an approximate translation into English of the relevant parts of Galluzzi’s presentation:

Galileo had performed an extraordinary operation. He had replaced a science based on the data of direct sensibility, the physics of Aristotle, along with its motionless earth and what our senses tell us: you see movement around you; qualities are intrinsic to matter; bodies are hot, cold, dry, hard, soft; objects fall because they are heavy. These are the evidences of common sense.

Galileo replaced this intuitive image, which was then the physics of Aristotle, with a science based on principles that overturned the impressions of sense: the earth moves, with two different movements, even if to us it is motionless, and our sense apparatuses do not show it. Bodies are made of homogeneous matter, yet they seem to us different from each other. Heat, cold, hardness do not belong to objects, but when we perceive them we feel heat, cold, hardness, impenetrability, and so on. It was a great revolution to replace a perceived nature with a thought-out nature, rationalized, geometrized. [Video from 35:29 to 36:42]

However, these passages also led to problems for Galileo with the Holy Inquisition of the Roman Church:

Rational structure of the world transparent to human understanding, Copernicanism, relativistic theory of motion, atomistic conception of matter and subjective analysis of sensations constituted an explosive mixture that completely blew up the tradition of knowledge. It is therefore not surprising that The Assayer drew the eye of the censors. Three complaints were sent to the Inquisition Tribunal immediately after the publication of the The Assayer. Anonymously, as was the custom. The first insinuated that from the work the author's Copernican sympathies were made clear. This accusation was correct, they did transpire, and the fact that he had disobeyed the decree issued by the church in previous years, which prevented those doctrines from being presented, was denounced.

The other two complaints focused attention on a more subtle and more delicate aspect. They believed that the theory of sensation Galileo outlined, namely that the primary qualities belong to the senses, not to nature, constituted a threat to a fundamental dogma of the Catholic faith, namely the mystery of the Eucharist, proclaimed dogma at the Council of Trent a few decades earlier…. Each time … the priest extracts the host from the monstrance, places it in the mouth of the faithful, offering him the wine to swallow it, according to Catholic theology, in each of those acts a miraculous intervention takes place. Thanks to this miracle, the bread of the host and the wine are transformed in terms of substance into the body and blood of Christ…, with the bread and wine retaining the color, texture and flavour of bread and wine. Where was the danger for this fundamental thesis if colour taste and smell are perceptions that belong only to us, i.e., they do not exist in nature? Where is the miracle of the transformation? Where is the miracle of the Eucharist in maintaining the qualities if the qualities are subjective and not objective, that is, in nature? [Video from 39:41 to 43:22, emphasis mine]

Fortunately for Galileo, when he was prosecuted by the Holy Inquisition some ten years later, it was only for the reaffirmation of his belief in the Copernican structure of the universe. If he had been pursued for violating the dogma of the Eucharist, his sentence could well have been much worse than the house arrest in his villa that was imposed upon him.

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1. Galileo Galilei. The Assayer. In Galileo Galilei, Horatio Grassi, Mario Guiducci, Johann Kepler. The Controversy on the Comets of 1618. Translated by Stillman Drake and C.D. O’Malley. University of Pennsylvania Press, 1960.

2. Alexandre Koyré. Galileo and Plato. Journal of the History of Ideas 4(4):400-428, Oct. 1943.