[forthcoming in The Journal of the History of Ideas]
1 Galileo‟s Interventionist Notion of “Cause”
In this essay, I shall take up the theme of Galileo‟s notion of cause, which has already
2received considerable attention. I shall argue that the participants in the debate as it stands have overlooked a striking and essential feature of Galileo‟s notion of cause. Galileo not only reformed natural philosophy, he also – as I shall defend – introduced a new notion of causality
and integrated it in his scientific practice (hence, this new notion also has its methodological
repercussions). Galileo‟s conception of causality went hand in hand with his methodology (see section 3). This is the main message of this essay. It is my claim that Galileo was trying to construct a new scientifically useful notion of causality. This new notion of causality is an
interventionist notion. According to such a notion, causal relations can be discovered by actively exploring and manipulating natural processes. In order to know nature we have to intervene in nature. Generally: If we wish to explore whether A is a cause of B, we will need to
establish whether deliberate and purposive variations in A result in changes in B. If changes in
A produce changes in B, the causal relation is established. It will be shown that this notion first emerged from Galileo‟s work in hydrostatics and came to full fecundity in his treatment of the tides.
Let me first of all take stock of the present discussion. De Motu is one of Galileo‟s early
scientific works on what we today would roughly call „mechanics‟ (written between 1589 and 1592). That in De Motu Galileo wishes to establish a causal explanation of motion (and
3 According to Galileo, falling bodies are moved by an acceleration) is accepted by all scholars.
4internal cause; projectiles by an external one. Galileo indeed claims that he wished to
determine the hidden causes of observable effects “for what we seek are the causes of effects,
5and these causes are not given to us by experience)”. In dealing with the cause of acceleration,
Galileo clarifies that he wants to discover the true, essential and not the accidental cause of
6acceleration. Acceleration is an accidental feature of motion, caused by the gradual overtaking of the intrinsic weight of a body during fall, after being lifted (and the weight being diminished) by an impressed force. Scholars begin to disagree however on the presence and importance of causal explanations in the period after this early work. Edwin A. Burtt, echoing Ernst Mach, wrote that Galileo‟s studies on motion led him to focus more on the how than on the why of
78motion. Closely connected to this is Galileo‟s ban of final causes from natural philosophy.
Galileo, according to Burtt, treated motions as the secondary causes of natural phenomena and the forces producing them as their primary causes (of which the nature or essence is further
910unknown). We only know quantitative effects of forces in terms of motion. This implies that
knowledge of primary, essential causes is impossible according to Galileo. After Burtt, authors have gone even further: they questioned the presence of causal explanation in toto in Galileo‟s
(mature) work. On the one side of the spectrum, Drake claims that Galileo banished causal inquiries from his science, since they were speculative and unnecessary:
The word cause, frequent in this early book, is less frequent in the later ones. It
played little part in Galileo‟s mature presentation of scientific material, which he
11confined more and more to observational and mathematical statements.
Causal claims were present in his early work (e.g. in the discourse on floating bodies (1612)),
12but not in his mature work (by which Drake apparently means the Dialogo and the Discorsi).
Pietro Redondi seems to side with Drake: Galileo was defending a docta ignorantia with
13 There are some passages which seem to converge to respect to causes and causal knowledge.
this interpretation (note that they can be made consistent with the causal interpretation as well). For instance, after having reviewed various hypothetical explanations of the cause of gravity, Salviati says:
Now, all these fantasies, and others too, ought to be examined; but it is not really
worth while. At present it is the purpose of our Author merely to investigate and
to demonstrate some of the properties of accelerated motion (whatever the cause
14 of this acceleration may be) (…).
Ernan V. McMullin, however, correctly argues that this passage in the Discorsi does not
necessarily mean a rejection of causal explanation: It simply means that dynamics needs to be
15preceded by kinematics. Only when the properties of motion have been described, can we start with explaining them causally. This does not necessarily entail a rejection of causal explanation as such.
On the other side, there are authors who stress the importance of causal explanation and causal reasoning in Galileo‟s work and relate them to past traditions where causal knowledge was important. Peter K. Machamer argued that Galileo‟s notion of cause is that of the tradition of the mixed sciences (“scientiae mixtae”):
I shall attempt to show that though Galileo does use such causal language with
serious intent, there is a sense in which Drake is right about Galileo‟s unconcern
for causes; Galileo is, for the most part but not all always, unconcerned about
extrinsic, efficient causes. This is one aspect familiar to those who deal with the
mixed sciences. Galileo is concerned very much with formal and final causes, and
16 sometimes material causes.
17He admits that his analysis is primarily based on the Discorsi. According to Machamer,
18proper (causal) explanations refer to formal, final and material (necessitating) causes.
19William W. Wallace has connected Galileo‟s notion of cause to the Aristotelian tradition.
Galileo frequently uses causal parlance which is in agreement with Aristotle‟s views of causes and his ideas on scientific method laid down in the Posterior Analytics. Galileo‟s scientific
demonstrations agree to and are derived from, as John H. Randall first argued, the regressus
20strategy in the Aristotelian tradition. Wallace‟s main message is that Galileo‟s nuove scienze
were not created de novo. Jacopo Zabarella was, as Randall claimed, “the methodologist who
21 Galileo continued to stood behind Galileo‟s early account of demonstrative methodology”.
22use the regressus throughout his career with various modifications.
23 Causal explanations are certainly present in Galileo‟s work. That is presently not the issue
The problem of causality in his science is clearly not whether he sought causal
explanations, but rather how he sought them and how he thought they could lead
24to certain and unrevisable knowledge about the physical world.
I would add to that list that in addition to this we also need to clarify what Galileo‟s notion of cause was. In this essay, I shall not directly evaluate Wallace‟s and Machamer‟s readings. My point is rather different: instead of solely focussing on past traditions from which much of Galileo‟s terminology appears to be derived, we should pay more attention to some of the innovative features of Galileo‟s notion of causality. There are prima facie parallels with past
traditions and indeed Galileo frequently used Aristotelian terminology. But, let us not equivocate Galileo‟s notion of „cause‟ with that of a past tradition too fast. Let us also look at
25 This is the aim of the present possibly original contributions of Galileo to the idea of cause.
essay: to point to the interventionist strand in Galileo‟s conception of cause.
In section 2 I shall therefore begin by carefully looking at some of Galileo‟s causal reasoning strategies. I shall discuss Galileo‟s treatment of the floating and sinking of bodies in water and his explanation of the tides. I have chosen these cases, because on these occasions Galileo is very explicit on his causal reasoning and his notion of „cause‟. These cases will pave the way for a more elaborate understanding of Galileo‟s notion of cause. In section 3, I shall compare
Galileo‟s interventionist notion of cause with James Woodward‟s recent theory of causation, presently one of the most developed interventionist accounts of causation. In the final section (4), I shall briefly point to the significance of Galileo‟s interventionist notion of cause in
26connection to the idea of what Antonio Pérez-Ramos has called an “active science”.
2. Galileo and the Occurrence of Physical Causes in his Scientific Work
In 2.1.1 and 2.2.1, we shall look at two case-studies in Galileo‟s works (one stemming from
the mid-period of his scientific career and one from his later work) where he explicitly discusses the notion of physical cause. These cases will give us access to Galileo‟s notion of cause. This will set the stage for a fuller discussion of Galileo‟s notion of physical cause in sections 2.1.2 and 2.2.2. The goal of this section (2) is to penetrate the deeper conceptual strata of Galileo‟s notion of „cause‟. I attempt to characterize Galileo‟s notion of “cause” in the form of three general statements, which are meta-level descriptions of Galileo‟s notion of “cause”.
2.1. The Emergence of „Cause‟ in the Discourse on Floating Bodies (1612)
2.1.1. Galileo‟s Causal intuitions in the Discourse on Floating Bodies
Galileo‟s discourse on floating bodies (first edition: 1612) was a best-selling book in its own
27 It is certainly time. Unfortunately, it has received relatively little attention by scholars.
relevant for an understanding of Galileo‟s notion of physical cause, since Galileo explicitly
addresses the problem of finding true causes. Stillman Drake suggests that, when Galileo first sharply defined the word “cause” for use in scientific inquiries, the “process by which causes
28gave way to laws in science may be considered as having begun”. In this discourse Galileo
refuted the Aristotelian explanation of floating. The Aristotelians, like Lodovico delle Colombe, asserted that bodies floated on water because of their flat shape which prevents its piercing the
29 Lodovico delle Colombe claimed to have refuted Galileo by water‟s resistance to division.
the following experimentum crucis: a flat ebony chip floats, while an ebony ball of the same
30weight cannot do so. The central tenet of the Aristotelians was water‟s resistance to division.
This tenet was based rather on the metaphysical assumption that all motion requires an
31opposing medium, and not on experiments. Galileo claimed – in agreement with Archimedes
– that “only greater or lesser heaviness in relation to water” is the cause of floating or
32sinking. Both parties claimed to have inferred the cause of floating bodies. How do we know what is the true cause?
Galileo, in defending his position, often argued about what a „(proper) cause‟ precisely is. In his notes early in the hydrostatic discussion (and not in the discourse itself), Galileo wrote that “Causa è quella, la qual posta, sèguita l’effetto; e rimossa, si rimuove l’effetto” (“Cause is that
33which put [placed], the effect follows; and removed, the effect is removed.” (sic)). This
definition seems to have guided him in his scientific research. Galileo set out to search for the
34 He “true, intrinsic, and entire cause of the rising and floating of some solid bodies in water”.wrote:
With a different method and other means I shall seek to reach the same conclusion
[as Archimedes], reducing the causes of such effects to principles more intrinsic