Dijksterhuis’s book The Mechanization of the World Picture surveys the history of the period during which this conception rose to hegemony, and in the Epilogue he considers several possible interpretations that the survey suggests. First, it is commonly said that a mechanistic conception of the natural world is one which sees it as a kind of machine, analogous to a clock. And such metaphors are, he says, indeed frequent in writers of the period.
However, Dijksterhuis does not think this actually captures what is essential to the mechanical world picture. The reason is that the notion of a machine implies teleology. For example, what makes a clock a clock is that it serves the function of telling time. It is true that this suggests a model of teleology that differs from the one associated with Aristotelianism, according to which natural teleology is intrinsic to a substance – in contrast to the teleology possessed by human artifacts, which is imposed from outside by their designers and users. (I have discussed the various conceptions of teleology in many places, such as this article.) All the same, the early modern mechanical philosophy was inspired by ancient atomism, which eschewed teleological explanation. And as the mechanical world picture developed, teleological explanations came to be seen as scientifically deficient. So, Dijksterhuis argues, the machine model does not really capture what is essential to it.A second
possible interpretation of a mechanical or mechanistic mode of explanation sees
it as essentially concerned with discovering the hidden mechanisms underlying natural phenomena. Think of the way that we come to understand
how an automobile engine works when we see how the burning of fuel creates
small explosions that move pistons, which in turn move the crankshaft, and so
on. Of course, such an engine is, like a
clock, a human artifact with its own distinctive teleology. But the teleology is not what is doing the
explanatory work on this second interpretation of what a mechanical explanation
amounts to. Rather, the idea is that
what illuminates our understanding is coming to see how the behavior of the
whole results from the arrangement and interaction of the parts as they push
and pull against one another.
The problem
with this interpretation, Dijksterhuis points out, is that not all explanations
that came to be regarded as mechanistic actually work this way. For example, Newton was never able to
identify a mechanism by which gravity worked.
And while some at the time were critical of his account of gravity
precisely for that reason, eventually it came to be regarded as a paradigm of
successful mechanistic explanation.
A third
possible interpretation considered by Dijksterhuis holds that a mechanistic conception
of nature is essentially “anti-animistic” in character, in the sense that it
rejects any explanation of a thing’s behavior in terms of some principle internal to it. Contrast this with Aristotle’s view in the Physics that what is natural to a thing
is precisely what does follow from an
internal principle. A mechanistic
explanation, on this interpretation, is one that explains a thing’s behavior in
terms of external factors (whether something pushing or pulling on it, the laws
that govern it, or what have you).
The trouble
with this interpretation, in Dijksterhuis’s view, is that there are mechanistic
explanations that do not operate this way, and Aristotelian explanations that
do operate this way. For example,
inertial motion seems to be motion that springs from an internal principle,
whereas Aristotelian theories of projectile motion appealed to an external
principle. Hence, this cannot be the key
to what sets mechanistic explanations apart from the Aristotelian explanations
they were meant to replace.
A fourth
interpretation takes mechanistic explanation to be explanation modeled on
mechanics, in the sense in which that term came to be used in modern
physics. And mechanics in that sense had
to do with explaining local motion in terms of a mathematical description of
the relations between objects and the laws that govern them. Newtonian mechanics became the paradigm, and
twentieth-century physics took the mathematical approach further still. This is the interpretation Dijksterhuis
endorses, so that he takes the mechanization
of the world picture to amount ultimately to a mathematization of the world picture.
In his
article on “Mechanistic explanation” in The
Cambridge Dictionary of Philosophy, philosopher of science David Hull
rejects this sort of interpretation, on the grounds that many physical
phenomena cannot be explained in terms of mechanics in this sense, but are
still thought to be in some sense explicable mechanistically. Hull writes: “Historically, explanations were
designated as mechanistic to indicate that they included no reference to final
causes or vital forces. In this weak
sense, all present-day scientific explanations are mechanistic” (p. 476 of the
first edition).
Crane’s
account of the mechanical world picture in his book The Mechanical Mind emphasizes both the rejection of final causes
and explanation in terms of mathematically formulated laws of nature. But he also says that pre-modern philosophy
and science were committed to an “organic” conception of nature, whereas
mechanical explanations reject this.
What he means is more or less what Dijksterhuis describes in the third,
“anti-animistic” interpretation of the mechanical philosophy. To common sense, a living thing seems to
operate according to an inner principle, which directs it toward a natural end
or final cause. Pre-modern Aristotelian
thought modeled inorganic substances too on these aspects of living
things. By contrast, the mechanical
world picture starts with inorganic things, understood as devoid of any such
internal principles or final causes. It
then seeks to model all of nature, including living things, on this way of
conceiving of the inorganic.
What should
we think of all this? On the one hand,
all of these suggestions do indeed capture themes that have historically been
associated with the mechanical world picture, even if some of them are more
central to it than others are. On the
other hand, it is not surprising that it should prove difficult to find a
precise and generally accepted definition.
The reason, I would suggest, is that from the beginning, the aim and
content of the mechanical world picture has been more negative than
positive. It is more about what it is
against than what it is for. And what it
is against is Aristotelianism.
In
particular, I would suggest, the idea of giving mechanistic explanations of
natural phenomena was always fundamentally about finding ways to make them
intelligible without reference to anything like substantial forms, intrinsic
teleology, and related ideas in Aristotelian philosophy of nature. The point was to replace this with an
approach that was simpler and allowed for the prediction, control, and
technological exploitation of natural phenomena. The other themes described above were natural
consequences of this.
For example,
machines have only accidental forms rather than substantial forms, and their
teleology or final causes are imposed from outside rather than intrinsic. Their behavior is also typically predictable
and controllable, and, naturally, they exist in order to serve the interests
for which we develop technology. If you
want a non-Aristotelian conception of natural objects that will be useful for
the practical purposes that interested early modern scientists and philosophers,
the machine is a natural model. Into the
bargain, it provided an alternative way to think of the world as dependent on
God – hence Aristotle’s notion of a prime unmoved mover gets replaced by the
notion of a divine machinist – which was important to thinkers who, for all
their hostility to Scholasticism, were still mostly theists (but became less
important as atheism became more common among the intelligentsia).
Since we
understand how machines work by determining what sorts of parts they are made
of and how those parts are arranged and interact with one another, it was only
natural that the mechanical world picture would initially not only think of
natural phenomena on the model of machines, but also think of physical
explanation as a matter of identifying hidden parts and mechanisms. Since the machines with which early modern
thinkers were familiar typically operated by means of parts pushing and pulling
on one another, it was natural that this crude sort of causation would for a
time also be a standard part of the mechanical mode of explanation. Since the teleology of machines and the
arrangements of their parts come from outside them – from the designers and
users of machines – it is only natural that the mechanical world picture would
initially think of natural phenomena as operating according to externally
imposed influences (motion imparted from outside, laws of nature, or what have
you) rather than something intrinsic to them.
Furthermore,
since the most impressive technologies are those that work with mathematical
precision (such as a well-made clock), it was also only natural that the
mechanical world picture would come to favor mathematical models of mechanisms
and mechanical processes. And this approach
would indeed go on to have spectacular success in allowing for the prediction,
control, and technological exploitation of natural processes.
In short, the initial motivation for the mechanical world picture was to develop a non-Aristotelian conception of nature that would facilitate certain practical goals; the machine model was the most promising candidate; that model in turn suggested several further themes, some of which did not last; but the theme of mathematization proved the most fruitful and thus survived and became the model for how to carry out mechanistic explanation. For this reason, as the mechanistic conception of the world developed, it essentially came to be about eschewing anything that smacked of final causality and substantial forms in favor of a mathematical mode of explanation that allowed for strict prediction, control, and technological application – with push-pull causation, the identification of hidden mechanisms, exclusive appeal to external principles of operation, and even the machine analogy itself eventually dropping away as inessential to the mechanical world picture.
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