299. Robert Pasnau on Substance in Scholasticism

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Bob Pasnau joins Peter to discuss ideas about substance from Aquinas down to the time of Locke, Leibniz and Descartes.



Further Reading

• R. Pasnau, Theories of Cognition in the Later Middle Ages (New York: 1997)

• R. Pasnau, Thomas Aquinas on Human Nature: a Philosophical Study of Summa theologiae 1a, 75-89 (Cambridge: 2002).

• R. Pasnau, Metaphysical Themes, 1274-1671 (Oxford: 2011).

• R. Pasnau (ed.), The Cambridge History of Medieval Philosophy, 2 vols (Cambridge: 2014).

• R. Pasnau, After Certainty: a History of our Epistemic Ideals and Illusions (Oxford: 2017).

Robert Pasnau’s website

Robert Pasnau’s blog on medieval philosophy: In Medias PHIL


Hristo on 10 April 2018

Substance and languages

That was a very illuminating conversation, thanks!

I wonder what is the most apposite term for substance in Ancient Greek philosophy - ousia or hypokeimenon or hypostasis? Perhaps this question is relevant to a possible correlate in the here upcoming Byzantine tradition? And in Arabic  - is the word for substance only a technical term or also in everyday use? Is it of Greek origin?


a true admirer of these podcast series

In reply to by Hristo

Peter Adamson on 10 April 2018


In Greek we are talking about ousia; hupokeimenon would be substrate or subject (I gather that Cicero actually invented the word "subiectum" as a literal version of hupokeimenon!). In Arabic it is usually jawhar, which is actually a loan word from Persian meaning "jewel". Latin of course is just substantia, which doesn't seem to render ousia at all but I guess the idea is that it is what "stands under" properties, but in a different sense than a merely potential substrate, like a substance is the bearer of accidental properties.

Hypostasis is more complicated, it kind of means "an existing thing" and was used with a technical meaning in Greek theology, notably in the Chalcedonian formula that says Christ was two natures in one hypostasis.

Otter Bob on 16 April 2018

A Couple of Questions

Prof. Pasnau says (beginning at 6:50) that it was fair to say that all the philosophers of this period thought that animals and other living beings are the paradigm cases of what are substances. I take it that means for them that, e.g., a limestone statue of a pope would be a substance but only in a way, not as a fundamental being. Even worse, the limestone boulder standing in the workshop before chiseling would be even less a substance. This is an ontological position and not just a statement about how they talk.

1) Was that the position of Aristotle?--that these, other types of beings, a natural but non-living entity or an artifact, are not substances, without qualification, even though any of them are hylemorphic compounds?

I never liked the translation of ‘ousia’ as ‘substance’. ‘Substance’ literally suggests what stands or is under something (hupokeimenon). Consider Hiawatha: She is a substance, a fundamental being. But we could ask: What is the substance of her? And the answer normally is “a giraffe”. But what is a giraffe? What is the substance of a giraffe? You see my problem. What is the substance of a substance? We can switch out the terms and ask: What is it to be a giraffe? Or what is the essence or nature of a giraffe? And it looks like Aristotle often uses ‘ousia’ in all these cases. But the essence of a hylemorphic being is its substantial form (‘eidos’ being the term most often used for what we translate as ‘form’).

2) How would Aristotle parse “the substance of a substance” without identifying ousia with eidos? Is it that Aristotle, and these thinkers in tow, would note that some terms are used in many ways (but pros hen) and that I’ve just made a muddle of this?

In reply to by Otter Bob

Peter Adamson on 17 April 2018


You probably won't be surprised to hear that Aristotle's position is a matter of debate but he does have the notion of a non-substantial "heap" e.g. just a pile of rocks or whatever that is not unified by any form. I tend to think that for him artefacts are full blown substances though some might deny this.

You are right that "substance" should not be taken to have the meaning of "substrate": but substance "stands under" something, because it is the bearer for properties, most obviously the accidental ones.

Aristotle of course has an elaborate discussion of what "primary ousia" is in his Metaphysics and there, it looks like the substance of substance, as you put it, is indeed the form (eidos).

In reply to by Peter Adamson

Otter Bob on 17 April 2018

Substance--a bit more

Thanks for the help.  

1) I know that Aristotle talked of heaps as non-substantial, but that is why I picked a clearly delimited and unified boulder.  I just have never come across a passage where he speaks of the ontological status of such.  Do you know of any?  I ask because it strikes me that Nature has many types of discrete and unified but non-living entities that bear properties.

2) Just to push it a bit farther:  We agree that at least in the Metaphysics he uses eidos for the substance of a substance.  But I was wondering about an argument that, despite the hylemorphic analysis, a substance is (one and the same as, nothing but) a form (eidos) once the potentiality [the matter] is actualized or enformed.  I'll leave that as a question.  I'm sure this has been discussed in the professional literature but I'm already in over my head.

In reply to by Otter Bob

Peter Adamson on 18 April 2018

More on substance

1. I think a boulder is a heap, for Aristotle - it has no intrinsic form that gives it a function, like an artefact or living thing, but is just a big chunk of earth. Obviously Aristotle is much more interested in living things, so that even artefacts have a somewhat unclear status, and I think naturally occurring nonorganic objects like these (boulders, oceans, mountains, clouds) are probably all heaps.

2. The issue in the metaphysics is precisely between the two options you are considering: is form the substance, or is substance the composite of form and (actualized) matter? And you're right that an ocean of ink has been spilled over this, but you have gotten the right question for sure!

In reply to by Peter Adamson

Otter Bob on 19 April 2018

Oh Well

1) So much for Aristotle. Don’t tell the collapsing mountain ledge that the boulder had no function (I’m kidding). But I am beginning to think that, for Aristotle (and me), Nature is not just the realm of change but paradigmatically the realm of changing living beings; they are the focal point.

2) Thanks a heap!  I’m trying to keep in the forefront whether a particular substance is its unity of form and matter or, more starkly, whether a particular substance is nothing other than its particular (substantial) form?  I was afraid I had gone a step too far out onto this ledge and, rather than being in over my head, was treading thin air by misreading Aristotle. Good to hear I'm not alone.  I think I’ll just keep talking with him and save the secondary sources for the lonliness and incapacities of old age.

Forward and Onward---------Otter

Petrus Ick on 21 April 2018

Substantially Informed

That was a fascinating discussion!
Just a few questions: Where does Aquinas discuss substantial form and put forward the views as discussed here? Is it in the 'Metaphysics' where Aristotle talks about this?
In Dr Pasnau's work do you know if he looks at Thomas Cajetan's views on the subject?
Also, I wonder how the mediaeval and early modern discussions on substantial form relate to current thinking in metaphysics and ontology.

In reply to by Petrus Ick

Peter Adamson on 22 April 2018


Glad you enjoyed it. For Aquinas' views on this the best place to look is his discussions of the human soul, both in the Summa Theologiae and Disputed Questions on the Soul. Actually Prof Pasnau's book Thomas Aquinas on Human Nature would be a great place to start, since it deals with the key part of the Summa.

He does discuss Cajetan in his big book mentioned in the interview, at least to some extent - I don't think he's one of the dominant figures in the narrative though.

As for the last question, maybe stay tuned for episode 300 part b, because we will be looking at the contemporary relevance of medieval philosophy in that one! For the substance issue I would say that there are attempts to revive Aristotelianism on substance and mereology, for instance in Kathrin Koslicki, so medieval discussions could be relevant for that.

In reply to by Peter Adamson

Pat Daley on 2 May 2018


I have listened to many of your history of philosophy podcasts, especially the Hellentistic philoosphers, because when i took a history of philosophy course many years ago, we sort of skipped them, as there are so recognized great philosophers among them.  Josepeh Owens' textbook, which is in many respects quite good, is an example.

I think a modern Thomist would say a boulder is a heap, but the minerals making it up would be substances.  It might be easier to think of the sea, which consists of water, various minerals, some dissolved gases, and various sorts of living things. Those constituents would be substances. I know some think the sea is a living thing, in a way, and Emerson's poem, Each and All, might be an example.

I do not think Dr. Pasnau's image of a bunch of matter works at all, since a bunch of matter would already have substances in it which have matter and form. A bunch of material would be subject to all sorts of accidental forms, such as rock being made into a statue, or canvas having paint daubed or splashed over it. I think matter and form works better in the arts, manufacture, and building.

One way of dealing with the persistance of the various elements of the body after death would be that the various elements, including minerals and scars, were there virtually while the person was still living and can continue after death.   I do not think prime matter would be anything independent, it is just the potentiality of substance to change substantially.  That never seemed very satisfactory to me, and so I tend to think of a hierarchy of forms (structures) in living things.

The process philosophers (i.e., Charles Hartshorne) seem to think substance in Aristotle is self-enclosed and could not act or be acted upon, as I recall.  This is clearly not what Aristotle thought, because he thought that the activity of the agent can take place in the patient, as when the teacher teaches the actual learning takes place in the students. I think Aquinas conceived the world as filled with active subtances, doing their best to communicate their being, in this respect similar to Plotinus. When he was 90, Hartshorne came to agree the had been wrong about Aristotle on substance.  Parenthetically, Hartshorne's actual occasions seem to be little subtances, just very short-lived ones. I am less impressed with Hartshorne than his fans are.

Keep up the good work, please!


In reply to by Pat Daley

Peter Adamson on 2 May 2018


You're certainly right that there is never any prime matter hanging around by itself without form. Prof Pasnau's point was that the particular bunch or chunk (call it whatever you want, but we want something vague because it has no features) of prime matter secures the individuation and continuity through change that we find in physical substances, at least on one popular medieval theory. So like my prime matter, while being featureless, would explain why I am distinct from other humans, e.g. on Aquinas' view (not on Scotus' though, for instance).

Your point about continuity through change, e.g. when a human dies, being explained by the fact that some material constituents are still present (minerals, elements etc) is right too and in fact that is the standard medieval view. But as Pasnau explains in the interview, and I also touched on this when looking at Aquinas in the podcast, Aquinas believed in the unity of form. So for him there is nothing at all in the human that is non-human, no actually present minerals or what have you. So your solution would not work for him.

Hope that helps?

In reply to by Peter Adamson

Pat Daley on 6 May 2018

Hi Peter,

Hi Peter,

I suppose it is difficult to explain prime matter, which actually has different interpretations.  One can start with acidental changes which occur with an enduring substance (like a stone, which can be shaped by a sculptor). But prmary matter does not seem to be something like Plato's receptacle or Plotinus' matter, which is why I suggested that the potentiality for substantial change belongs in the substance.

I am aware that Aquinas held to the unity of substantial form.  How this really works for gold or limestone, which exist in many different pieces, I don't know.  But in living things like humans, the substance includes everything in us, though we are always breathing out air and carbond dioxide, sloughing off pieces of our outer skin, sweating, etc., so the boundary is vague.  As for continuity in death for a while, and breaking down into various compounds, Aristotle and Aquinas were quite familiar with that, along with everyone else. I do remember a professor who remarked that the different elements and chemicals are virtually within us, which I took to mean that they acted like the elements even though under the form of humanity.

Now, you may think that Aquinas cannot account for this since he held to the unity of the substantial form.  I confess that previously, I had never really looked into this, and I never got around to asking that professor what that virtual presence was.  But it was an easy search, actually, and I found an artilcle which shows that Aquinas (and maybe even Aristotle) were well aware of this problem, and that Aquinas did his best to answer it.


It would only seem fair to present what Thomas said about this issue.  

A few years ago, I bought  The One and the Many by the late Fr. W. Norris Clarke, S.J.,  subtitled A Contemporary Thomistic Metaphysics, U. of Notre Dame Press, 2001, not that I ever read all of it, because he had written on process philosophy and knew Charles Hartshorne. Process philosophy is one of my  bête noires as far as interpreting Aquinas goes and in its conceptions of God.  I also wanted to see if Fr. Clarke was confused on essence and existence.  Anyway, in Ch, 9, p.  144-45, he actually discusses the "Rival Franciscan School: plurality of substantial forms." If I had read the whole book, I would have seen that.  He does not reject the plurality of substantial forms outright, but thinks Aquinas' view is preferable.

"It should also be noted that even the scientific evidence now gives increasing support to St. Thomas's unicity theory by revealing how lower elements inside a higher complex being do not act just the way they do outside such a being on their own."

I think the plurality theory with a series of hierarchical forms could account for that, too, but the debate still goes on.

I do think you should have mentioned what Aquinas said on the virtual presensce of elements in a complex being. One needs to be careful with Thomas, because when you object to something, you may well find he had discussed the objection somewhere.

I look forward to listening to new podcasts and the many I have not yet heard. The HOPWAG is truly a remarkable project and I hope you will be able to keep it up into modern philosophies.

In reply to by Pat Daley

Peter Adamson on 6 May 2018

Unity of form

Hi - thanks for the thoughtful response. Maybe Pasnau and I concentrated, on this interview, mostly on the counterintuitive aspects of Aquinas' view but of course you are right that he defended it in detail. I actually discuss that in episode 244 at some length. I think your point that the elements are only "virtually" present in the still living organism is, however, not so much a point in his defense as a rephrasing of why the view sounds so crazy. I mean, the objection to him is precisely that on his account elemental or non-organic parts of the body are only virtually present in the living body and then - hey presto! - suddenly become actually present upon death. Thus they all need to go from mere potential to actual being, which is quite puzzling, and it isn't clear that they have identity over time through that change, as Pasnau pointed out in this episode. As I say in the earlier episode, number 244, a better point in his favor would rather be the other one you make here, namely that lower level constituents are taken up into organic parts, like for instance internal organs.

In reply to by Peter Adamson

Pat Daley on 6 May 2018

Unit of form

LOL I am not sure "sounds so crazy" is a proper philosophical argument, but point well taken!



Zarl on 15 May 2019

Renaissance conservatism

I'd be interested in hearing more about the condemnations mentioned here, which caused philosophy to become more timid and conservative (contrary to what most people believe) between the 14th century and the 17th, sticking to Aristotle especially in natural philosophy.

From what I read elsewhere, this was actually due to the dominance of Humanism during that time, which was reactionary in nature and tended to discourage any thinking that couldn't be considered in line with the Ancients. But perhaps there'll be more about this in the Renaissance series.

Simon on 31 March 2024

Decomposing as thomist

Could you argue the fact that  the body decomposes in time, After death, as defending a thomist perspective 

In reply to by Simon

Peter Adamson on 31 March 2024

Thomist decomposition

No I don't think so; the problem is that the instant you die, according to Aquinas a different substance comes to be that was not there before. For form pluralists, the substance that is a human is also a body and has both forms. So when the human form is lost, the bodily form persists, and there is no absolute destruction and coming to be - a substance persists through the change, namely a body, which was there both before and after death. Aquinas has to have the body sort of leap into existence from mere potentiality at the moment of death, which is an odd claim. What happens after that with rotting away is not really relevant, I don't think, because it is about this moment of change at death. Does that make sense?

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