The Contributions of John Philoponus

Thank you for pointing out John Philoponus. I was unaware of his contribution to the concept of inertia well prior to Galileo.


Philoponus’ contributions were massive.

  1. First and foremost, he overthrew Aristotle’s entire scientific paradigm, an achievement which wasn’t recognized for centuries later and which no one else managed to do until around the fifteenth century. Aristotle’s science had to die in order for real science to progress.

  2. He introduced the experimental method, actually testing his theories with physical modelling. Almost no one else did this systematically until the late medieval era.

  3. Without the aid of a telescope, he not only determined that the stars were large fires (contrary to what Aristotle and everyone else believed), but also determined that their brightness and color indicated their size, age, and chemical composition (stellar spectroscopy wasn’t a real science for about another 1,200 years).

  4. Several groundbreaking contributions to physics, including the all important principle of inertia.

Someone needs to make a movie about him, he’s a virtual unknown yet he was influential on a string of subsequent important medieval, Renaissance, and early modern thinkers, including Ibn Sina, Bonaventure, Gersonides, Buridan, Oresme, Gianfrancesco Pico della Mirandola, Galileo, and Newton.


Philoponus’s early critique of Aristotelian physics is certainly of significance (though arguably it had little influence on thought for many centuries, and arguably the same critique would have emerged in late medieval Europe even without his writings), but it hardly warrants the sweeping claim that Philoponus was “a more formidable contributor to Western intellectual history” than Aquinas. Philoponus’s contributions were limited to the area of natural science, whereas the thought of Aquinas has influenced many fields. One may not like Aquinas, but one has to acknowledge his titanic influence on the Western mind. Otherwise, one’s comments on the history of ideas, the history of philosophy, history of religious thought, etc. are simply not credible.

Methinks the commenter’s hostility to Aquinas is impairing his historical objectivity.


It’s more accurate to say that it had a significant effect on those who read it. It obviously had no effect on those who didn’t.

Arguably, on what basis?

No they weren’t. His works “Against Proclus on the Eternity of the World” and “Against Aristotle on the Eternity of the World” were both towering works of philosophy, in which his natural science emerged as a byproduct. Likewise, his work on impetus emerged as a byproduct of the arguments in his theological treatise “On the Creation of the World”, as an explanation of how God started the movements of the planets. Philoponus did philosophy and theology first, natural science second.

His philosophical commentaries on Aristotle’s “Categories”, “Prior Analytics”, “Posterior Analytics”, “Metaphysics”, “Meteorology”, “On Generation and Corruption”, and “On the Soul”, were translated into Syriac, Arabic, and Latin, and influenced Christian, Jewish, and Muslim interpretations of these works for centuries.

Historians of philosophy study Philoponus’ impact on both the Western and Muslim philosophical traditions, all the way up to the Renaissance. Historians of science study Philoponus’ impact on both the Western and Muslim traditions of natural science, all the way up to the early modern era.

In contrast, historians of philosophy study the impact of Muslim philosophy on Aquinas, and historians of science study the impact of Muslim natural science on Aquinas, and speak of “Aquinas’ reliance on Islamic thinkers”.

In your opinion. If we removed Philoponus from history, then the entire history of science would be different. If we removed Aquinas from history, the impact would not be comparable. Philoponus made an objectively measurable impact on the Scientific Revolution, of which the modern era in which we live is a product. Aquinas did not. Incidentally, if we removed certain Muslim philosophers from history we might not even have many philosophical works from Aquinas.

The scope of his influence is not in dispute in this thread.

I don’t have any hostility towards Aquinas.

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A link:

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Oh, no, none at all:

Sounds like hostility to me. Maybe not personal hostility, but certainly intellectual hostility.

Yes it is, and you are the one who disputed it. You spoke of contributions to “Western intellectual history” – which history includes more than science, and more than metaphysics, and more than commentaries on Aristotle which have gone mostly unread by anyone but specialists for over a thousand years; Western intellectual history includes philosophy, theology, science, law, political theory, ethics, aesthetics, and many other things. And you said that Philoponus was “far more formidable” in his contribution to that history. But Aquinas’s thoughts on theology, philosophy, war, ethics and many other matters entered into the mainstream of Western discourse and debate, and have helped to shape Western culture for centuries. Philoponus’s influence at the beginning of modern science may have been considerable at a key juncture, but his writings are not read now by anyone but academic specialists in history of science or history of philosophy. Aquinas’s thoughts helped to shaped the later theology of the Roman Church, and of other churches (there are many Anglican Thomists, for example, and even Calvin read Aquinas with great attention and respect), and his thoughts on natural law, war, human nature, etc. went into the mainstream of Western thought. His writings are still commonly read not just in Catholic institutions but in secular Great Books programs throughout the world. His overall contribution to Western culture is greater and more pervasive than that of Philoponus. That does not denigrate the contribution of Philoponus. There is no need for you to belittle Aquinas in order to praise Philoponus. But you seem determined to take shots at mainstream, historically orthodox, non-sectarian forms of Christianity at every opportunity.


I don’t know about the other claims, but Philoponus did not come up with inertia, rather the theory of impetus. Philophonus’ impetus is very different from inertia, and regardless the theory of impetus was already “discovered” ~600 years before Philophonus by Hipparchus.


Yes we both mistyped, it should have been impetus not inertia. The impetus theory was the necessary foundation of the modern inertia theory.

That’s a little misleading. Hipparchus had “a” theory of impetus. However, even Aristotle had “a” theory of impetus, around 500 years before Hipparchus. But we don’t use Aristotle’s theory of impetus today, and we don’t use Hipparchus’ theory of impetus today either. Likewise, Ibn Sina, Ibn-Badja, al-Bitruji, abd Barakat, all had “a” theory of impetus, but we don’t use their theories of impetus today.

Hipparchus’ view of impetus was a “potential impetus” which differs from the modern conception. The modern concept of impetus is built on Philoponus’ view. As I have already pointed out, Philoponus didn’t do all the work; his view of impetus was developed in important ways by his successors (Oresme in particular). But it is his view of impetus which is the core of the modern understanding. Key figures in the modern understanding of impetus (such as Galileo and Newton), had to break with both the Aristotelian and Hipparchan view.

Yes, I misspoke there.

I suppose this is where I disagree: we don’t have a modern understanding of impetus, as the theory of impetus is not used in modern physics. The modern concept of inertia is very different from any understanding of impetus, be it Hipparchus’ or Philoponus’, and I really don’t see how the idea of impetus is at all a necessary foundation of modern inertia theory.

Maybe it’s a matter of preferred terminology.

  • “Philoponus had introduced the un-Aristotelian idea of ‘impressed power’, which has been compared to the modern theory of impetus” (Oxford Handbook of Aristotle)

  • “Philoponus is not impressed by these arguments, and offers a new theory, which has been compared to the modern theory of impetus” (Philosophy in the Hellenistic and Roman Worlds)

  • “Under his influence Parisian scholars came close to the modern theory of impetus” (Europe in the Sixteenth Century)

  • “One of the most celebrated achievements is the theory of impetus, which is commonly regarded as a decisive step away from an Aristotelian dynamics towards a modern theory based on the notion of inertia” (Stanford Encyclopedia of Philosophy)

I really don’t see how the idea of impetus is at all a necessary foundation of modern inertia theory.

It isn’t. I said it was necessary for people like Galieo to break with the Aristotelian view of impetus in order to arrive at a modern understanding. The modern view of inertia could have come about in a manner which didn’t involve the development of impetus theory by scholars such as Philoponus or Buridan, but I don’t think Galileo and Newton could have arrived at a modern view of inertia by holding to Aristotle’s view of impetus.

I agree, there is some terminology difference here than what I am used to. My suspicion is that philosophers might like to use the word impetus to refer to what physicists call inertia, as all the links you provided are from philosophy instead of physics. I have never seen the word impetus used in lieu of inertia in physics publications.

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Why are we just debating the definition of terms by referencing encyclopedias? It would be much more enlightening to actually get into the scientific content of Philoponus’ theory of inertia and see how it differs from inertia in modern physics.

It’s something like this:

Philoponus: When something causes an object to move, that something also bestows the object with a “motive power” (like some sort of fuel) that causes the object to keep moving. This motive power (like fuels) run out after a certain amount of time and the object stops moving then.

Modern inertia: The object itself has a property that resists changes in its motion. In particular, a moving object will keep moving in the same motion forever unless forced to change its motion.


Finally you’re getting it. You quoted me criticizing his metaphysics and theology, when you were supposed to be supporting your claim of my alleged hostility towards Aquinas. Criticism of his metaphysics and theology is not hostility towards him.

No. I didn’t say anything about the scope of his influence being small. I commented on its significance in comparison with that of Philoponus. I made the point that in my view contributing to the Scientific Revolution was a more formidable contribution, since it had a far greater impact; our entire modern society is based on the Scientific Revolution, which cannot be said of Aquinas’ metaphysics, philosophy, or contributions to theology, ethics, and law. As I pointed out, if we removed Philoponus from history the entire history of science would be different. If we removed Aquinas from history, what would the impact be?

I said Philoponus made a far more formidable contribution to Western intellectual history. I identified these specifically as scientific contributions, not any other field. I certainly never claimed Philoponus’ contributions had a wider scope than Aquinas’; I said they had a greater impact.

You’re creating a false equivocation. In the case of Aquinas you cite not only his direct influence (in terms of who read his work and who still reads it), but also his intellectual legacy and indirect influence (however diffuse), through the people who read, interpreted, and responded to his work. yet in the case of Philoponus you cite only people who read his original works, and not his intellectual legacy or indirect influence. This is not a valid comparison.

It’s significant that most of your description of Aquinas’ contributions is confined to theological debates within a few Christian sects. This is not equivalent to Philoponus, whose influence on science impacted several different fields and was not confined to special interest groups. An assessment of Philoponus’ impact cannot be confined to “Who reads his original works these days?”, but must take into account his intellectual legacy and impact on philosophy and science. Historians of science and philosophy take this into account, but you do not.

In mainstream public schools, students are taught laws of physics to which Philoponus contributed; they are not taught about Aquinas’ theology. The entire field of stellar spectroscopy is founded on Philoponus’ initial observations; Aquinas contributed nothing comparable.

They did indeed, and I even cited a couple of them previously. In another thread, Joshua is musing about what kind of theological justification could have been used for the savagely cruel treatment of indigenous people such as the Tasmanial aborigines. One simple answer is “Thomism”. Aquinas’ views on natural law, war, and slavery, were explicitly used to justify the conquest and barbarous treatment inflicted on the indigenous people of South America. Since you’re so interested in the legacy of Thomism, you really need to confront its appalling historical impact, to which I alluded previously. I wonder if you can lay any equivalent atrocities at the door of Philoponus?

I am not doing this.

What nonsense.

This is interesting, would you mind elaborating? Do you claim that if Philoponus does not exist, we won’t have stellar spectroscopy? As a professional astrophysicist who is very familiar with stellar spectroscopy and its history, I find this quite an unbelievable claim.

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I described it previously. Philoponus determined that the different colors of stars indicated that they were composed of different chemicals, which produced different colored light as they burned. He didn’t know or speak of wavelengths, but he knew from observation that different chemicals burned with different colors, and rightly concluded that since the stars were fires then their different colors were attributable to the different chemical compositions of the materials they burned.

Of course I am not attributing the entire modern understanding of stellar spectroscopy to him, only one of the foundation concepts.

No, not at all, not in the least, not remotely, not in any way. No. Also, no. When I write A, I mean A, not B. We went through this previously, when I made a comment about Philoponus’ contribution to the development of inertia, and you asked me if I was saying we wouldn’t have a theory of inertia if it weren’t for Philoponus. My answer was an emphatic no. Now you’re asking the same kind of question again, and I don’t know why. In case it’s unclear, my answer in this case is also no. I don’t understand why you keep making these leaps.

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Does any fan of science history ever attempt such an argument? This is a rather extreme accusation, and one that @Jonathan_Burke will be able to say with great confidence: “No, of course not.”




I was just asking because you claimed that

I hope it’s understandable how that statement seems at odds with

Edit: also, this

is not right at all, and is not what is referred to by stellar spectroscopy.