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Sitting on the moon?

In a recent blog post, Dennis des Chene replies to reflections by Mohan Matthen on the question whether some common sense intuitions may be resilient to refutation through science. In this context, Dennis comes up with an interesting thought experiment. Imagine a man sitting on the moon with his head pointing towards the Earth. For Dennis, the Aristotelian, it is clear that he is then “committed to holding that […] my feet are above my head (‘above’ being understood Aristotelian-wise); […]”. And this is meant to be true, because ‘up’ and ‘down’ are absolute notions (for an Aristotelian).

Graphics courtesy of Nadine Michael

Of course the idea that I’m sitting on the moon and have to assume that my feet are above my head seems to be pretty counterintuitive. But is it really? After all, we must take into account that sitting on the moon and facing the Earth is a fairly uncomfortable situation, at least for Aristotelians. Humans are made of two elements, earth and water. Both these elements tend to move towards the center of the universe. So it seems that the natural posture for Aristotelians on the moon is this:

We can see, everything is in order here: My feet are beneath my head, the moon is above it. The idea that my feet are above my head when sitting on the moon isn’t as far-fetched as it seems, as soon as it is clear that sitting on the moon is a posture against nature - as much as a headstand on Earth.

Now imagine that the Aristotelian on the moon looses his grip and falls towards Earth.. The following passage from the Physics gives us an idea of what should then happen:

ἔστι δὲ τὰ τοιαῦτα οὐ μόνον πρὸς ἡμᾶς, τὸ ἄνω καὶ κάτω καὶ δεξιὸν καὶ ἀριστερόν· ἡμῖν μὲν γὰρ οὐκ ἀεὶ τὸ αὐτό, ἀλλὰ κατὰ τὴν θέσιν, ὅπως ἂν στραφῶμεν, γίγνεται (διὸ καὶ ταὐτὸ πολλάκις δεξιὸν καὶ ἀριστερὸν καὶ ἄνω καὶ κάτω καὶ πρόσθεν καὶ ὄπισθεν), ἐν δὲ τῇ φύσει διώρισται χωρὶς ἕκαστον. (208b14-19)


Nor do such distinctions (up and down and right and left, &c.) hold only in relation to us. To us they are not always the same but change with the direction in which we are turned: that is why the same thing may be both right and left, up and down, before and behind. But in nature each is distinct, taken apart by itself.


For Aristotle, spatial terms express properties of substances rather than relations between substances, even though the common sense presumes the exact opposite. But this means that ‘natural place’ is determined not only with respect to ’ up’ and ‘down’, depending on the proportion of elements in the thing in place. Rather, substances have a natural ‘right’ and a natural ‘left’.

Johann Paschius defends this thesis in his 1685 dissertation “De loco”:


Paschius discusses two arguments for his view:

1. The argument from geographic orientation:

In II De Caelo, Aristotle teaches that movement of the spheres originates ‘on the right’ and all other cardinal points can be derived from that.

Idem alibi docet [sc. Aristoteles] dextrum id esse, unde principium motus est; hinc facile reliquas Loci differentias in Mundo à natura positas reperies, videlicet Ortus dextrum, Occasus sinistrum Septentrio faciem, Meridies dorsum, Zenith verticem, Nadir pedes cinget atque teget.

Moreover, in another text Aristotle teaches that the right is, whence the principle of motion comes from. Therefore, you will easily find the other differences of place as they have been posited by nature: the east encompasses and covers the right, the west the left, the north the front, the south the back, the zenith the top, the nadir the feet.

What Pasch seems to argue here is that there is a natural position in the world for human bodies: Facing north is more natural than facing south.

2. The argument from the spatial organisation of organisms:

[…] quod natura in ipsis animalibus hoc tam accurate observet, ut partibus singulis certum assignet locum et situm, huic dextrum, illi sinistrum, isti superiorem, alteri inferiorem; hanc retrò, aliam anté collocet. Si autem in quibusdam individuis earundem transpositio eveniat, illa pro monstris habentur.

[…] nature takes this [observer-independence of spatial properties] into account very accurately, as far as animals are concerned: She assigns a place and position to bodily parts, for this [sc. part] the right, for another the left, for this one a superior (sc. position), for another an inferior one. One part is placed at the back, another one in front. If in some individuals parts are transposed, such individuals are taken to be monsters.

The intuition behind the idea that there is a natural right-hand side of an organism is not as far-fetched as it seems at first glance. Imagine a teacher in front of his class, asking them to rise the left hand. This will always mean the left hand from the pupil’s point of view.

What does all this mean as far as the Aristotelian hanging from the moon is concerned? Imagine that he falls towards the earth. Aristotle’s theory of natural place (and natural non-relational local properties) suggests that it is more natural to land on one’s feet than on one’s head. Additionally, we should expect that our nose points towards the north, whereas our back-side points southwards.

But this landing position cannot be explained, or so it seems to me, by natural forces. The mixture of elements in a human body only explains the plain fact that it tends to fall towards the center of the earth. But how do we account for the fact that the spatial orientation of the body in falling (and landing) seems to be predetermined as well?

Stefan Heßbrüggen-Walter

  1. emto posted this
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