Husserl on Galileo and the Primary and Secondary Quality Distinction

Last week’s nitpicky post (here) on Husserl’s treatment of Galileo generated a number of polarized (mostly private) emails: some felt I had been unfair to or misleading on Husserl, while others thought I was not critical enough. I am afraid today’s post is also nitpicky—although of wider philosophical and scientific interest, and so may generate a similar response. To the friends of Husserl, I say that, first, I intend to do a less critical post before long (on the way Husserl anticipates some features in Thomas Kuhn’s meta-philosophy); and, second, my critical remarks below do not threaten the core of Husserl’s own project.

Today’s post is on Husserl’s treatment of Galileo on the primary vs secondary quality distinction and, more importantly, on the relationship between that distinction and the geometrization of nature in The Crisis of European Sciences and Transcendental Phenomenology: an Introduction to Phenomenological Philosophy (first published in 1954) in David Carr’s (1970) translation (Northwestern University Press). Strictly speaking neither Galileo nor Husserl use that phrase to describe the distinction in immediate context, but that’s how it came to be known to us.¹

To simplify what is about to follow: Husserl claims that the primary vs secondary quality distinction is a necessary effect of, or at least a natural by-product, of the geometrization of nature. And the thought is that once one geometrizes nature, one necessarily starts to treat the geometric qualities of bodies as primary and real, and the non-geometric bodies as secondary and also not quite real. A view like this is not silly, but I don’t think it is right historically or philosophically.

That is, one can hold a version of the distinction between primary and secondary qualities without being committed to geometrized nature or vice versa; nor that it is quite right to attribute it to Galileo—this despite the highly salient seeming fact that Galileo articulates his version of the distinction in the Assayer, which is also the text in which he offers his famous claim about the book of nature being written in geometry. In fact, I would claim that the primary-secondary quality distinction is a by-product of people holding variants of corpuscularianism and that it isquite orthogonal to the geometrization of nature.

For example — well it’s controversial — Spinoza holds a version of the primary quality distinction (see, e.g., Letter 9 to Simon de Vries),² but as Alison Peterman has argued (in two famous essays one from 2014 (here) and another from 2015 (here)) it is not obvious that he holds that geometric properties are features of bodies as such (rather than, say, the effects of abstraction). It is also not evident that for Spinoza extension is (say) Euclidian in character. That is, what this example shows is that what drives commitment to variants of the primary vs secondary property distinction is not geometrizing nature, but his corpuscularianism, which is described in his own voice in the so-called ‘physical interlude’ of Ethics II.

So much for set up. Here’s how Husserl puts his own position in David Carr’s translation.

With Galileo’s mathematizing reinterpretation of nature, false consequences established themselves even beyond the realm of nature which were so intimately connected with this reinterpretation that they could dominate all further developments of views about the world up to the present day. I mean Galileo’s famous doctrine of the merely subjective character of the specific sense-qualities, which soon afterward was consistently formulated by Hobbes as the doctrine of the subjectivity of all concrete phenomena of sensibly intuitive nature and world in general. The phenomena are only in the subjects; they are there only as causal results of events taking place in true nature, which events exist only with mathematical properties. If the intuited world of our life is merely subjective, then all the truths of pre- and extrascientific life which have to do with its factual being are deprived of value. They have meaning only insofar as they, while themselves false, vaguely indicate an in-itself which lies behind this world of possible experience and is transcendent in respect to it. (pp 53-54; II.i)

Before I get to the primary-secondary quality distinction, I have quoted the whole paragraph so readers have a sense of what is at stake in Husserl’s diagnosis. As the last few lines make clear, something of immense value (what Husserl elsewhere calls the ‘life-world’) is lost if we take the geometrization of nature as more than a method. In fact, just before Husserl had diagnosed the nature of the problem as follows, “It is through the garb of ideas that we take for true being what is actually a method—a method which is designed for the purpose of progressively improving, in infinitum, through “scientific” predictions, those rough predictions which are the only ones originally possible within the sphere of what is actually experienced and experienceable in the lifeworld.” (pp. 51-52, II.h; emphasis in original.) So, we are not deprived only of important value(s) toward the ordinary life-world, and lead a life of error (confusing a means of learning about reality with nature as such), we also end up having the wrong comportment within science. Lurking here is a larger story made familiar by Thomas Kuhn about the way scientific puzzle-solving creates a form of cognitive alienation within science. But that’s for another time.

Okay, with that in place, let’s turn to Husserl’s treatment of Galileo (and Hobbes). Now, it’s correct that for Galileo the secondary qualities are not real, being merely in subjects as a result of the effects of primary qualities. As Galileo puts it (in Stillman Drake’s translation), “tastes, odors, colors, and so on are no more than mere names so far as the object in which we place them is concerned, and that they reside only in the consciousness.” I should say that Drake’s use of ‘consciousness’ is misleading. As Filip Buyse noted in a very fine (2015) paper (p. 31), it would be more literal (and accurate) to say that for Galileo they reside only “in the sensible body.”³ Keep that in mind.

Either way, in the Assayer, Galileo dramatically suggests secondary qualities would vanish if humans would disappear: “if the living creature were removed, all these qualities would be wiped away and annihilated.” And so Husserl’s main concern that Galileo treats the primary qualities as real in a way that the secondary qualities are not, and thereby devalues the latters, is definitely correct.

But it is not quite right that for Galileo the primary qualities are real in virtue of their geometric properties or exist qua geometric properties. Here’s how Galileo puts his own position, “whenever I conceive any material or corporeal substance, I Immediately feel the need to think of it as bounded, and as having this or that shape; as being large or small in relation to other things, and in some specific place at any given time; as being in motion or at rest; as touching or not touching some other body; and as being one in number, or few, or many.” Now, if one is thinking of Descartes here (for whom extension is geometrical) or Kant’s Euclidian intuition then one may be tempted to read Galileo’s list of characteristics of material substance in geometric fashion. But when you look closely, you’ll note some properties of the corporeal substance need not be geometric in character not the least time and motion and the rather vague terms of ‘few’ or ‘many.’ Of course, one can read all of these in terms of quantity, so I am not denying that this way of treating primary qualities facilitates the “mathematizing reinterpretation of nature.”

In fact, when Galileo discusses a few of these properties, he does not emphasize the geometric properties of ‘touch,’ but rather the sensation it generates in humans, including pleasure: touch “though it exists over my entire body, seems to reside principally in the palms of the hands and in the finger tips, by whose means we sense the most minute differences in texture that are not easily distinguished by other parts of our bodies. Some of these sensations are more pleasant to us than others.”

So, rather than treating the distinction as a by-product of the geometrization of nature, I think of it is as a by-product of a corpuscularian analysis of nature in which such corpuscules generate sensation in certain kind of bodies. And in this account corpuscles in motion are the causes of effects in nature and in sensitive perceivers. If sensitive bodies were removed the titillation would be removed, too: “This titillation belongs entirely to us and not to the feather; if the live and sensitive body were removed it would remain no more than a mere word.” I was pleased to see that my treatment of this is in accord with the spirit of Buyse’s treatment of Galileo’s account of the primary vs secondary quality distinction.⁴

To be fair to Husserl (and leaving aside the odd example of Spinoza), it’s fair to say that prior to the Principia most lists of primary and universal qualities are compatible with treating these qualities as somehow geometric in character. Geometry is not merely a language to convey one’s science in it, it is somehow (partially) morphic with the structure of true reality. But as Biener and Smeenk have documented in an eye-opening 2012 paper, in the Principia the geometric conception of matter was complemented and fundamentally overshadowed by a more ‘dynamic’ conception of matter. While geometry and mathematics remain useful in studying nature, once space and matter are conceptually separated, there is no reason to assume that matter is constituted by geometric properties.⁵ (This, in turn, is orthogonal to the kind of arguments that the skeptics about the primary vs secondary quality distinction started to marshal, but it clearly prepared the way for them.)

In fact, once Newton argued his way into treating gravitational force as a universal quality of matter without it being reducible to or required by the geometric properties of matter, and treating mass as a universal, albeit highly abstract quantity that is an abstract property of all matter, the connection between the geometrical conception of nature and matter is severed. Yet, when in the Opticks, Newton articulated his version of the primary vs secondary distinction in discussing the properties of rays that produce colored vision, his corpuscularianism is never far from the surface since the rays propagate the motion of corpuscles (see the definition to Prop II, theory II).

1. In Appendix II “Idealization and the Science of Reality” Husserl uses the more familiar nomenclature.

2. Melamedoff, Ariel. “Neutral Monism and the Attributes of God in Spinoza’s Metaphysics” Archiv für Geschichte der Philosophie. https://doi.org/10.1515/agph-2023-0187

3. Buyse, Filip. “The distinction between primary properties and secondary qualities in Galileo Galilei’s natural philosophy.” Cahiers du Séminaire québécois en philosophie moderne/Working Papers of the Quebec Seminar in Early Modern Philosophy. Vol. 1. 2015.

4. Buyse does downplay the role of ancient atomism in Galileo’s account of the distinction, but that does not undercut my main point.

5. My own rather radical view is that even in Newton’s most Cartesian document, DeGrav, Newton does not require space to be Euclidian. But that’s for another time.