For Aristotle, the so-called sublunary sphere consists of the classical four elements, fire-water-earth-air. It is the realm of ever-changing things in contrast to the part of the universe which begins with the moon and stretches to the fixed stars and in which everything is made from the fifth element, the quintessence or aether, and so is incorruptible and eternal, never deviating from its regular and periodic motion.

But there is some counter-evidence to this theory that can be gained by unaided observations of the night sky.

  • If we look at the full moon with the naked eye, in normal circumstances, we can see at least the lunar maria, maybe, if we have good eyesight, even a big crater like Clavius.

    How did Aristotle explain that the lunar maria are darker than the highlands if the whole moon is made from aether? How can an object made out of this perfect material have such blemishes?

  • And then there are shooting "stars", which are transient and changing. Yes, they are "sublunary", of course. But how could Aristotle have known this?

  • Visible comets are not "sublunary" and while they have regular orbits (but with very long periods), there is no such cyclical change in brightness (as observed with the Moon).

  • Finally, there are variable stars (stars whose brightness as seen from Earth changes, an extreme example would be a supernova). As stars they would have been located in the outermost celestial sphere, and so clearly made out of aether. There is some evidence that variable stars were observed in 1200 BCE by Egyptian astronomers.

Was there some criticism of the "aether theory" along those lines by Aristotle's contemporaries? Did Aristotle try to give justifications how this counter-evidence is reconcilable with his theory?

  • I think it might be more prudent to start with was Aristotle aware of any counterarguments based on data to his aether theory? To which I think the answer is that we don't have many other extant text than his own which tell us what he knew / didn't know and (as far as my memory goes) he's not aware of any of the criticisms you list. (you can find it out in more detail by reading BK I of each of his works on physical science -- since BK I usually surveys known theories).
    – virmaior
    Commented Jan 2, 2017 at 10:11
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    About comets, see : Tofigh Heidarzadeh, A History of Physical Theories of Comets, From Aristotle to Whipple, Ch.1 Aristotle's Theory of Comets. Commented Jan 2, 2017 at 10:55
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    @MauroALLEGRANZA thanks a lot. The link even explains what Aristotle thought about shooting stars. You could easily make an answer out of your four comments.
    – viuser
    Commented Jan 2, 2017 at 12:02

2 Answers 2


In general, Aristotle's approach to science was not the modern one: he was a very good "observer" (mainly in zoology and biology) and thus his approach is clearly "emprical", but :

(i) in A's science there is no concept of "testing" a theory, trying to verify/falsify it through especially designed experiments:

(ii) in A's science there is no concept of "prediction" of new (unknown) phenomena.

The focus of Aristotle's science is understanding, i.e. locate all known phenomena in a general theoretical framework in order to explain them, according to the theoretical framework of Aristotle's philosophy: substance, actuality and potentiality, the four causes, etc.

More specifically, regarding "imperfections" on the Moon's surface, still with Galileo's telescopic observations available, the main "Aristotelian" explanantion was : shadows, atmospheric clouds, earthly "exalations".

About comets, you can see :

  • According to the Duhem non-falsifiability thesis (“if the predicted phenomenon is not produced, not only is the questioned proposition put into doubt, but also the whole theoretical scaffolding used by the physicist”), your point "(i)" is true for modern science, too.
    – Geremia
    Commented May 22, 2017 at 3:11

The sublunary spehere that you're referring to is due to Aristotles cosmology.

But there is another sense that A uses it, and this is in his Physics, where he theorises physical concepts, and there the sublunary sphere is the sphere where change occurs - he names it as the proper object of knowledge for the scientist; it ought to be contrasted with the sphere where change does not occur; although it refers to the moon, its not really about the physical moon; a contemporary example would be field theory which isn't really about the fields you find in the countryside.

  • Thanks for this answer, very interesting. On the face of it, this seems to be a very idiosyncratic interpretation (but the downvote was not from me!). Who else did interpret Aristotle this way? Can you give a reference or two? Or what would be a quote from Aristotle that supports your interpretation?
    – viuser
    Commented Feb 23, 2017 at 23:03
  • @wolf-revo-cats: try reading the very first paragraph in Aristotles Physics; it's a primary reference. Commented Feb 23, 2017 at 23:14

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