40 - Let's Get Physical: Aristotle's Natural Philosophy

Posted on 3 July 2011

Before Isaac Newton (and Olivia Newton John), there was Aristotle. Peter looks at his Physics, focusing on the notions of actuality and potentiality and how they help to explain such concepts as time and motion.

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Further Reading

• D. Bostock, Space, Time, Matter and Form (Oxford: 2006).

• U. Coope, Time for Aristotle (Oxford: 2005).

• L. Judson (ed.), Aristotle’s Physics: A Collection of Essays (Oxford: 1991).

• B. Morison, On Location: Aristotle's Concept of Place (Oxford: 2002).

• F. Solmsen, Aristotle’s System of the Physical World (Ithaca, NY: 1960).

• S. Waterlow, Nature, Change, and Agency in Aristotle’s Physics (Oxford: 1982).

Stanford Encyclopedia: Aristotle's Natural Philosophy

Comments

John 26 November 2014

Excellent entry, as usual! One small correction: Morison's book is _Aristotle's Concept of Place_ (not Space).

Peter Adamson 26 November 2014

In reply to by John

Oh, right you are! Ironic since I am usually very careful to say "place" in this context rather than "space." I'll change it now.

ALD 20 July 2015

On the first page of Physics it says: "We think we know a thing only when we have grasped its first causes and principles and have traced it back to its elements." Where in his lecture notes does he state the first causes and principles of the elements themselves. Doesn't it all point to a single element, the One.  And yes, if there is just one principle,  then there are no principles, just the One - this makes complete sense.  

Well, from the fact that we need to go back to first principles, it doesn't follow that there is only one first principle. There could be e.g. one first principle for motion, another for colors, another for human beings, another for logical argument, another for musical proportion etc - different principles for different sciences. Having said that, Aristotle does recognize a very important first principle in his Metaphysics, namely God - though it is much disputed how much God is supposed to explain in his system. I would be skeptical though of the idea that God (or anything else) plays in Aristotle the role of a unique first principle that eliminates the need for all other first principles.

Ian Favell 1 September 2015

Peter and All, hi.

My enquiry concerns Aristotle’s contention that simple bodies possess a single motion that is appropriate to them. The context is book one of Copernicus’ work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Orbs), 1543. Copernicus wants to show that the Earth, understood to be a sphere, possesses, like the known planets - including Sun and Moon - circular motion, contrary to the established model of the cosmos. Is it contrary, however, to Aristotelian physics? It would appear, based upon the formulation of his question that Copernicus believes it may not be, although given his evident familiarity with Aristotle’s natural philosophy seen throughout book one perhaps there is a little ‘politics’ at play here. Nevertheless, does Copernicus have a point or not? Is for Aristotle a particular type of motion associated, as Copernicus implies, with a specific form or with an object’s composition?

(We can infer that Copernicus is alluding to Aristotelian physics both because Aristotle’s natural philosophy dominated this field of study at the time and because it was chiefly Aristotelian scholars that he had to convince of the validity of his cosmological theory even if finally it contradicted certain, but not all, principles of Aristotelian physics. Aristotle’s physical principles are specifically identified elsewhere throughout the text and are even retained by his theory.)

Chapter 5:

Now that the earth too has been shown to have the form of a sphere, we must in my opinion see whether also in this case the form entails the motion, and what place in the universe is occupied by the earth.

 

We note that in chapter 4 Copernicus stated: “the motion of the heavenly bodies is circular, since the motion appropriate to a sphere is rotation in a circle.” Nevertheless, Aristotle in On the Heavens, Book I, 2, states: “It necessarily follows that circular movement, being unnatural to these bodies [the four elements], is the natural movement of some other . . . therefore, we may infer with confidence that there is something beyond the bodies that are about us on this earth, different and separate from them; and that the superior glory of its nature is proportionate to its distance from this world of ours.” Given that the Earth is composed of the four elements, which are characterized by constant change or generation and decay it would appear that for Aristotle its substance is unsuited to circular motion, irrespective of the Earth’s admittedly spherical shape. Indeed, in Book I, 3, Aristotle says, “The body, then, which moves in a circle cannot possibly possess either heaviness or lightness. For neither naturally nor unnaturally can it move either towards or away from the centre”, but these are precisely the characteristics of the four elements of which the Earth is composed. Copernicus continues:

Chapter 8:

Why then do we still hesitate to grant it [the Earth] the motion appropriate by nature to its form rather than attribute a movement to the entire universe, whose limit is unknown and unknowable?

And

Why should we not admit, with regard to the daily rotation, that the appearance is in the heavens and the reality in the earth?

 

As in Chapter 5, Copernicus is again suggesting that the Earth’s spherical form indicates circular, and here rotational, motion as befitting that form. It is evident that for Aristotle, however, an object is considered befitting of circular motion by virtue of its composition not of its form, specifically, that of the fifth element or ‘aither’, which is eternal and indestructible, unchanging and like the circle without beginning or end.

Does Aristotle indicate elsewhere that this is not so? (I have not seen evidence of this in the Physics, Metaphysics or On the Heavens.) Has Copernicus simply misunderstood Aristotelian physics, as his contemporary Giovanni Maria Tolosani (1470/1 - 1549) asserted? I would be surprised if this were so and suspect something else is going on, but I cannot be sure.

Thanks for this very interesting comment. I can't claim much expertise on Copernicus (though I look forward to covering him on the podcast at some point). But I think I can give you Aristotle's answer: the special thing about the heavens, which shows that they are incorruptible and made of a fifth element, is not that they are spherical in shape/form but that they _move_ in a circular fashion. The sublunary elements don't do this; they move "up" (i.e. away from the cosmic midpoint) or "down" (towards it). The shape of the earth is actually not natural to it but an accidental by-product of this rectilinear motion: because earth is trying to get to the midpoint from all directions it forms a sphere (same for the other three sublunary elements). This is explained in On the Heavens and is well understood in medieval times, actually there is even a little treatise by al-Kindi on why the elements form spheres, which explains it in these terms.


Hope that helps!

Peter, hello.

Thanks for the response. I could see from On the Heavens, why Aristotle considered the Heavens special and the relevance for him of circular motion, but I must admit I had not appreciated that the Earth was only spherical accidentally and could thus be distinguished from the planets in this way, even aside from its actual composition; yes, I have read what Aristotle said of the shaping of the Earth by virtue of the linear motion of its elements, but in a Cosmos that has no beginning there is no reason to assume that the Earth had a beginning and so a period of formation leading to a sphere. So, sphericity as an accident; interesting.

Ian.

Yes, you're right that earth has always been where it is. But actually somewhere (probably in On the Heavens but I forget) Aristotle entertains a thought experiment: what if earth were moved away from the centerpoint? And he says it would naturally re-form as a sphere around the centerpoint as I suggested in the previous comment. So that passage might be worth tracking down for you.

Peter, hello again.

Certainly, if you can find that passage I would be interested to read it; I would be particularly interested to know to what purpose Aristotle intended to put this thought experiment. As it happens, today, whilst working on Copernicus, I had reason to read Book II, 10 of Aristotle's On the Heavens, which may perhaps bear upon this issue: the translation I am using is that of J.L. Stocks. Aristotle is here concerned to show "that the movements of the several stars depend, as regards the varieties of speed which they exhibit, on the distance of each from the extremity." (Since the stars associated with the sphere of stars are fixed I take it for granted here that Aristotle is referring to the 'wandering stars' or planets.) These bodies move in the opposite direction to the heavens or outer sphere of stars; the bodies closest to that sphere are the most strongly influenced by it and so move the slowest, whilst those bodies farthest from that primary sphere are the least influenced and move the fastest. I have not had a chance to think about this passage in detail and so I don't want to say too much now, but I could not help but wonder if the behaviour here described might have a bearing on how the Earth would behave.

Ian.

JD 17 October 2015

If you watch the movie closely, you'll notice that Leeloo is not herself the fifth element. She is an embodiment and representation of it (just as the four stones embody and represent the four classical elements). Each of the stones must be activated by their related element in order to release their power. Similarly, Leeloo's power can only be released when activated by her associated element. Her power is activated when Korben admits he loves her. The fifth element is love, which brings things together and opposes the chaos-inducing element of strife. What a moment for an Empedocles reference!

Point taken, but as you know I'll usually sacrifice a bit of accuracy for the sake of a joke. I look forward to a sequel featuring Strife!

Ian 19 April 2016

Peter, hello.

The following has, due to other matters, been a long time coming, but it is an unexpected observation I could not lay aside so here it is.

Aristotle's De Anima, Book II, 7: (trans. by J.A. Smith)

"Neither air nor water is transparent because it is air or water; they are transparent because each of them has contained in it a certain substance which is the same in both and is also found in the eternal body which constitutes the uppermost shell of the physical Cosmos . . . fire too contains something which is one and the same with the substance in question."

(Emphasis my own.)

Does the element earth, then, also contain this substance that is found in the "eternal body"?

Peter, you have explained previously that “the special thing about the heavens, which shows that they are incorruptible and made of a fifth element, is not that they are spherical in shape/form but that they move in a circular fashion. The sublunary elements don't do this,” but move up or down.

Thus, if it is circular motion that implies the existence of a fifth element it would seem to follow that this element would be unique to the superlunary sphere. If, however, the above translation is accurate it would seem that the Earth and the superlunary sphere (the region from the Moon to the stars) share that element and are not as distinct as Aristotle I think elsewhere, such as in ‘On the Heavens’ (De Caelo), indicates them to be.

Perhaps we should not be entirely surprised by the apparent presence of the fifth element within the elements that compose the Earth given that it too in Aristotle’s cosmology is eternal: how could that which is corruptible or subject to decay, which the Earth is held to be, exist eternally unless it were possessed of something that was not so susceptible to change?

Ian.

Thanks for that interesting post - I meant to look up the Greek of the passage today at work, but forgot, so for now let me just tell you what I suspect/assume is the case. The translation you have there must be misleading. When it says that a "substance" is held in common this presumably doesn't mean that in Greek a stoicheion (element, i.e. something like the four elements or aether) is common between earthly and celestial realms - Aristotle certainly does not think that. Rather it means that a feature, i.e. transparency, is common to both aether and certain sublunary elements, like air: the aether of the spheres must be transparent since they are surrounding the earth but they aren't visible, except for the stars embedded in them. Does that set your mind at rest?

By the way later philosophers, notably Philoponus, denied that the celestial bodies are made out of a special fifth element; but as I say Aristotle argues forcefully for this claim.

Ian 21 April 2016

In reply to by Peter Adamson

Peter, hi.

Without any further evidence one way or another I cannot be sure what Aristotle intended to say in the said text: as I indicated it did seem to contradict Aristotle's 'On the Heavens' (De Caelo), but I am also aware that authors may express different views at different times (consider the changes in Newton's gravitational theory during its development) so I cannot rule out that possibility simply because it is inconsistent with explanations given elsewhere. If you are able to produce a translation of the Greek text yourself I would be most interested to read it. Would you by any chance know how far apart in time De Caelo and De Anima were written?

Your suggestion that Aristotle intended to say that a common feature, not an element, was shared between the sublunary and superlunary spheres sounds plausible, but it does beg the question, what is the cause of that quality? Did Aristotle explain how two entirely different physical objects could both possess a common property without physically sharing anything in common?

Ian.

Peter Adamson 26 April 2016

In reply to by Ian

I had a look at the Greek of your passage. The key word here is "nature" (phusis) which is a very broad term, I would take it here to mean something like "feature" or perhaps "innate feature." So the point is not that there is some kind of stuff (an element, or substance) common to air/water and the heavens, but rather that both have the "nature" = feature of transparency. Hence I would translate the key sentence as follows: "such [i.e. transparent] are air, water, and many other solids; for it is not insofar as they are water or air that they are transparent, but because there is a nature present in both of these, which is also present in the eternal, upper body."

Aristotle's theory of the transparent (to diaphanes) is rather complicated, but basically it means the capacity to receive light and color. Surprisingly, in De Sensu he explains the color of visible objects in light of "the transparent" in them, so the idea seems to be that the color of something depends on its degree of transparency i.e. its capacity for being actualized by light. Obviously this suggests that diaphanes does not really mean "transparent" in our sense (i.e. it doesn't mean something you can see through). Transparent media like air have the ability to become illuminated and then serve as a medium for vision - the reason that the medium itself isn't visible, like a colored body, is according to Aristotle that it has no limits or boundaries the way a body does. So, as I say, rather complicated and strange from our point of view, but certainly there is no suggestion here of a material commonality between the sublunary elements and the heavens.

By the way it isn't really surprising that the heavenly body might have some feature in common with some sublunary elements despite being made of completely different stuff: just consider that the heavens are also solid and extended, like a rock. That shouldn't incline us to think that they share a type of material with rocks.

Ian 26 April 2016

In reply to by Peter Adamson

Peter, hello.

Thankyou for a most interesting commentary, to which I will certainly give further thought. I am still looking closely at Galileo and his works and the historical context in which they are set and of course Aristotle’s cosmology and philosophy were very much a part of that.

Many thanks,

Ian.

Patrick The Fencer 3 May 2018

First off, thank you so much for putting out this podcast.  It's a really lovely presentation of the material and delights this classics nerd turned lawyer's heart.  

Second, I really enjoyed this particular episode, and will be recommending it to a group of people who at first blush one might not suspect: fencers.  

I study historical fencing to keep me out of trouble, and starting in the late 16th century, Italian and Spanish rapier fencing, each in their own ways, used Aristotle's physics, in particular his understanding of time to talk about time in sworfighting.  Having a philosphy professor clearly explain what Aristoltle thought makes it much easier to understand the fencing manuals of Salvator Fabris or Pacheco de Narváez.  Pacheco and the Spanish tradition even label downward motions of the sword "natural" since the earthy sword is moving as nature would have it move towards the earth.  

Peter Adamson 4 May 2018

In reply to by Patrick The Fencer

Wow, now that is an application I really never considered! That's a fascinating example of how far Aristotelian philsoophy penetrated into medieval and Renaissance culture. Thanks for bringing it to our attention!

Alexander Johnson 24 April 2019

I know you didn't discuss the falling objects thing in this episode, but it is in this book and I have a question on it.  Conventional wisdom holds that Aristotle believed a heavier object falls faster than a lighter object, at speeds proportional to the weight of the object, and that no one challenged this assertion until Galileo.  This seems absurd to me, and like it does not need an established high effort experiment to disprove.  In fact, it would have a ton of counter-examples available just in every day life (a barrel dropped on a hill will accelerate as it falls, vs have a fixed speed.  a rock slide in mountainous Greece would have the small rocks fall at hte same speed as heavy objects.  a small pebble and heavy rock bumped off a desk at the same time will hit the ground certainly not take a 100 to 1 ratio to fall compared to one another.  not to mention that i'm sure a heavy man and light man have raced each other to the bottom on hills on sleds/carts while drunk long before the rennaisance) .

So I wonder, what is Aristotle's theory on this?  When was it first challenged?  and assuming it is wrong, when did the misconception first occur? (at the very least, fall acceleration would be proportional to density, rather than speed to weight.  or potentially, terminal velocity in a medium would be proportional to density)

Peter Adamson 25 April 2019

In reply to by Alexander Johnson

Well that is actually a long story. There are a number of later episodes where I touch on this, including especially the ones on Philoponus and 14th c physics, though it also comes up in the Islamic series now and again. If you go to the list of "Themes" below and go to the episodes on physics, you will see a lot of relevant installments.
 

Emily 26 April 2019

In reply to by Alexander Johnson

This was an amazing paper! Thank you so much for posting a link to it.

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