Monday bonus: Jean De Groot, Mechanics in the Fourth Century BC
Claims about Aristotle’s meanings, simple machines, the M-inference and movements in equilibrium
Jean De Groot wrote:
Chapter 1
Empiricism and Mathematical Science in Aristotle
Powers and Mechanical Philosophy
The action-enhancing features Aristotle observed in both simple machines and living things contributed to his great confidence in deploying the dunamis concept widely in his philosophy.
[Dunamis = 'potency', 'potential', 'capacity', 'ability', 'power', 'capability', 'strength', 'possibility', 'force' and is the root of English words dynamic, dynamite, and dynamo]
Once this connection is suggested and then bolstered by textual evidence, it seems very reasonable. Indeed, my argument is that the very mundane familiarity of experiences of mechanical advantage and disadvantage ensured that phenomena of this sort would play an important role in Aristotle’s science. This need not be a contentious point. A philosopher could acknowledge it and perhaps still maintain that it has very little to do with Aristotle’s real philosophy, his logic and metaphysics. So, why has the physical base for the dunamis concept not been recognized before? One reason is the received historiography of mechanics. Mechanics is the invention of modern science. Before the early modern period, there was only a rudimentary theoretical understanding of simple machines and a few fragmented analyses of the balance in the Middle Ages. This part of the historiography has a certain amount of truth to it, in part because of the poor survival rate of ancient texts in mechanics and mathematics. The problem has been the alliance of this judgment with another, namely, that the mathematical science of mechanics appropriately issues in a single philosophy of nature, the mechanical philosophy. In the mechanical philosophy of nature, matter is all of the same kind though divided into tiny parts, which are either atomic or infinitely divisible. Differences in things originate from the size, shape, speed, impact, and accidental coherence of atoms. Power is replaced by force, the rigidity of bodies, and motion as causes. …
Fortunately, recent scholarship undertaken in a variety of venues is probing the meaning of “mechanism” in the history of science and gives reason to question the inevitability of the alliance of mechanics with mechanical philosophy. Indeed, it has become clear that early modern developments in mechanics were fed by rediscovery of the ancient accounts of simple machines. The mechanical philosophy came later … It is important to recognize that in matters of natural philosophy the division between practical and theoretical was not rigid for Aristotle and his school. Aristotle understood that machines work as they do because of underlying natural principles.
Automata in Plato and Aristotle
The idea that the animal or human body is a machine, or works like a machine, is associated with the mechanical philosophy of the early modern period. Though connotations of the machine-model vary with the author, it is basically Democritean: shape, arrangement or disposition, and linkage of parts define the unity of a functioning body. Methodologically, the aim is to reproduce living phenomena by artifice. Simulation proves causation. Both Plato and Aristotle spoke of animals and their parts by alluding to automata and linkage of parts, though considerably less often than we find in early modern texts. As might be expected, their aims in citing simple machines were quite different from those of Descartes, for instance. Yet, Aristotle for his part did not simply borrow automata to be a model for the powers of natural things. … I will avoid use of the term “model” in discussing references to automata in Plato and Aristotle. This is because their own command of the issues of likeness, illusion, and analogy reached deeper than simply taking man-made self-movers as either imitations or epistemic models.
For understanding the role of machines in ancient philosophical thought, the word “device” is a better translation of the Greek word, μηχανή, than “machine”. Device may mean either
a. contrivance, i.e., construal or arrangement of existing things in a way that makes them instrumental to an otherwise unrealizable end, or
b. the instrument made by contrivance.
Plato and Aristotle tend to take the two meanings together. They were quick to see a link between the simplest device, like a wooden simulacrum on a stick [the puppets], and more complex contrived phenomena, like automata. This is a sign that they were not simply trying to explain natural things as machines. Device was a source of enlightenment, a disclosure of reality that was otherwise inaccessible. In device, the distinction between the real as given (phusis) and what else can come from the real demands attention.
Chapter 11
Aristotle’s Empiricism in Cognitive History
The Fundamental Insight of Mechanics
[The] very spare inference to a principle of change is … a feature of early modern mechanics in its most economical expressions and was very intentionally made an element of classical mechanics by a succession of its practitioners in the 17th–18th centuries: a change in a movement has some origin.
This formulation –– a change in a movement has some origin –– is open either to an ontological or a minimalist interpretation, depending on whether one takes the origin as a force (or cause) or simply as a function (placing the change within a system or structure). I believe that the minimalist version of this inference is the core empirical insight that Aristotle gained from ancient mechanics. It guided his natural philosophy.
I assign to the inference characteristic of mechanics the shorthand moniker, M-inference. …
… We know forces through the effects of forces. Furthermore, forces are known precisely as the effects they bring about. …
… The M-inference is, however, too basic to implicate inevitably a single philosophical position. It is simply minimal. The lesson is that inference to force from action taking place precedes ascription of causes or characterizations of force. … Indeed, addressing Aristotle himself, someone might say that, surely, there are many sources for a notion so basic as “change requires a principle of change”. One could, for instance, find a predecessor of the notion in Anaximenes’ introduction of condensation and rarefaction
as the source of differences in a natural world composed from aetherial air. Anaximenes is responding to the rational problem “Why does the one existing substance change? Why does it show different appearances?” Anaximenes’ answer could be viewed as substance-based — the one thing compacts and disperses –– and thus not reliant on something inherently dynamical, like proportional rules. …
… It is possible to establish ancient recourse to the style of inference I have highlighted by consulting Aristotle’s own works and works of his school. As one would expect, the M-inference shows itself in the Aristotelian Mechanics. In that treatise, of the three terms –– ischus, dunamis, and rhopê –– ischus and dunamis are used more or less synonymously to mean force, a push, or an immediate external source of movement.
The act that is ischus or dunamis is intelligible in terms of the movement it brings about, which is represented in the mechanical conception of the Aristotelian Mechanics by lines of different lengths. Rhopê, on the other hand, is a more nuanced term in Mechanics. It connotes the influence due to position, weight, and added force, which will initiate movement or suffice to alter a movement underway. So, whereas ischus and dunamis are thought of as uncombined and individuated acts of agency, rhopê is an accumulated or combined power of movement at the point of its beginning to show itself. To this extent, the phrase “moment of force” is a useful and apt placeholder for rhopê, which has the connotation of a tipping point of influence. An example of this meaning of rhopê is the discussion in Mechanics 8 of how a balance beam situated vertically will move when disturbed. The author is discussing why larger circles are moveable with little effort.
Further, he who moves circular objects moves them in a direction to which they have an inclination as regards weight (ᾗ ῥέπει ἐπὶ τὸ βάρος). For when the diameter of the circle is perpendicular to the ground, the circle being in contact with the ground only at one point, the diameter divides the weight equally on either side of it; but as soon as it is set in motion, there is more weight on the side to which it is moved, as though it had an inclination in that direction (ὥσπερ ῥέπον). Hence, it is easier for one who pushes it forward to move it; for it is easier to move any body in a direction to which it inclines, just as it is difficult to move it contrary to its inclination (τὸ ἐπὶ τὸ ἐνάντιον τῆς ῥοπῆς). ([Aristotle] 851b26–33)
In this passage, the author treats inclining (rhepein) or inclination (rhopê) as an additive influence productive of movement. Points on a circumference are understood as being inclined downward due to weight on either side of a vertical diameter. In this condition, the inclination due to weight is equally balanced on either side of the diameter (851b29). A point at the top of the vertical diameter is thereby unmoved. If a mover adds inclination by pushing (ὠθεῖν) along the circumference (a push operating along the tangent to the circle), the effect is equivalent to adding weight to an already existing but equally balanced inclination (b30–31). By means of rhopê, the author gives an account of why circular movement turns out to be so useful in the crafts. As soon as the wheel is set in motion, it is after that easier to move forward by additional pushing. The force exerted (ischus) need not be so great. This is because its inclination is already in the direction of the manifest movement. Rhopê is a conception of a confluence of inducements to movement, which are made intelligible by means of perceptible effect.
Looking to Aristotle’s own works, we can see that he makes use of a similar inference. Movements or activities, changes in movement, or transitions from rest to movement are prompts for inference to a principle. In Physics IV.8, Aristotle says repeatedly that differences in the movement of the same body signal some difference in at least one of the factors sustaining the movement. … As one part of this reductio, he says that movement without an impediment operating against it will continue indefinitely (215a20–22). The coincidence is due to the fact that Aristotle too is thinking in the terms of mechanical notions available to him that concern changes within a system of movement. He is also thinking of force being correlative to perceived effects. In any case, the insight means that, if a medium affects movement by slowing it down, the absence of force will entail a movement continuing always at the same rate of change.
A cognate of the M-inference is the inference to an origin or a principle, archê, which is so much a part of Aristotle’s method. …
[Arche; Ancient Greek: ἀρχή; sometimes also transcribed as arkhé) is a Greek word with primary senses "beginning", "origin" or "source of action" (ἐξ ἀρχῆς: from the beginning, οr ἐξ ἀρχῆς λόγος: the original argument), and later "first principle" or "element". By extension, it may mean "first place", "method of government", "empire, realm", "authorities" (in plural: ἀρχαί), “command". The first principle or element corresponds to the "ultimate underlying substance"]
… [The] inference to a principle (archê), and the M-inference … most lucidly portrays the minimalism of Aristotle’s method of thought. This minimalism, as an aspect of later classical mechanics, came to characterize the method of mechanics above all else.
Whenever it appears, the M-inference is involved with another feature of reasoning in mechanics. This feature runs throughout the mechanical references in Physics IV.8 and could be called the equilibrium-sum rule (ES):
ES: Factors contributing to movement, whatever they are, participate in a system in which energy and movement taken together maintain some version of equilibrium.
One feature of ES replicated in Aristotle’s inferences to archê is that any natural subject or phenomenon under consideration participates in a system of activity or movement. This is important to note, because the intelligibility brought into a situation by the archê or gnômôn is more than the opposition and separation of naming. In Aristotle’s equilibrium-sum reasoning, it is not force or energy in heterogeneous kinds of things — movers, moved things, speeds — that is mutually interchangeable. That is, force is not passed along and transformed in its different subject matters. Rather, the equilibrium itself assumes many different forms. If one thinks within this picture of systematic relation, while avoiding the mistake of making force the interchangeable element, then one needs a strong rationale for tracking equilibrium as present similarly across different subject matters. Equilibrium (isorrhopia), like archê, is a notion that serves explanation in physics while remaining at a remove from physical things themselves or the concepts of physical things. …
The Source:
Jean De Groot, Aristotle’s Empiricism : Experience and Mechanics in the Fourth Century BC, Parmenides Publishing 2014
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