166 - Tamar Rudavsky on Gersonides and Crescas

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Tamar Rudavsky joins Peter to talk about the two great medieval Jewish thinkers after Maimonides: Gersonides and Crescas.



Further Reading

• T. Rudavsky, “The Theory of Time in Maimonides and Crescas,” Viator 11 (1980), 289-320.

• T. Rudavsky (ed.), Divine Omniscience and Omnipotence in Medieval Philosophy, (Dordrecht: 1985).

• T. Rudavsky, Time Matters: Time, Creation and Cosmology in Medieval Jewish Philosophy, (Albany: 2000).

• T. Rudavsky and S. Nadler (eds), The Cambridge History of Jewish Philosophy: From Antiquity to the Seventeenth Century (Cambridge: 2009).

• T. Rudavsky, “Christian Scholasticism and Jewish Philosophy in the Fourteenth and Fifteenth Centuries," in D.H. Frank and O. Leaman (eds), The Cambridge Companion to Medieval Jewish Thought (Cambridge: 2003).

• T. Rudavsky, Jewish Philosophy in the Middle Ages: Science, Rationalism, and Religion (Oxford: 2018).


Peter Adamson on 9 March 2014

Sound quality

Apologies for the sound quality on this one which is not great - it was recorded over Skype.

Maciek Zajac on 9 March 2014

Still I think it was a pretty good one

Episodes on Crescas were definitely most intresting among the Jewish philosophy ones.

If I may have a question on a much earlier topic - what Greek expression would Plato use to render the meaning of "moral/ethical knowledge"? Would Aristotle use a different expression? One of my friends remembers that in the metaphor of the cave Plato discerns four levels of knowledge the escaping philosopher reaches, each time using a different word. Would the appropriate expression be phronesis? Epsiteme with an adjective? Or something different still?

In reply to by Maciek Zajac

Peter Adamson on 9 March 2014

Moral knowledge

Glad you liked Crescas. I kind of knew about him before writing the episodes so to me the big revelation was actually Ibn Paquda, whom I'd never read before.

Re. your terminology question I think (though maybe there is a passage I am not thinking of in Plato) that phronesis is defined as a specifically practical faculty first in Aristotle. In the passages where Socrates proposes an identity between virtue and knowledge he just calls virtue an episteme. It's right that Plato gives four kinds of cognition in the divided line, the top ones being noesis (all the way at the top) and then dianoia, which the Neoplatonists understood to mean respectively pure intellection and discursive thought. Neither of these seems to refer exclusively to theoretical or practical wisdom; indeed it would probably be fair to say that Aristotle's distinction between those two goes against the spirit of Plato's epistemology, which tends to see practical wisdom as intimately related to "theoretical" knowledge (i.e. grasp of the Forms).

In reply to by Peter Adamson

Maciek Zajac on 10 March 2014

Thanks a lot

That was very helpful :)

Tom Roche on 10 March 2014

Crescas and Augustine

Correct me where wrong, but ...

In episode 166, Rudavsky says, and you concur, that "of course" Crescas didn't know Augustine. But

* before that (IIRC) she maintains, and you concur, that both Crescas and Gersonides were engaged with the Scholastic tradition
* the Scholastics (e.g. Aquinas) are seriously into Augustine
* Augustine is one of the more Jew-friendly Church Fathers (granted, not stiff competition :-)
* Crescas is born ... what ... 900 years after Augustine dies?

Sooo ... why "of course"? Am I missing something? And, speaking of missing something: given

* Rudavsky's @ OSU
* you're from NJ
* your demonstrated inability to resist comic opportunities however minor

I am shocked (shocked!) that you did not sign off episode 166 with, "goodbye, Columbus" :-)

In reply to by Tom Roche

Peter Adamson on 10 March 2014


Oh, that's a very good point. I guess we would have to sort out whether it is likely he could have read the Confessions, which is rather a different proposition than, say, chatting with Ockham. But at least indirect influence could definitely be there if he is exposed to scholasticism.

Sorry to miss the joke opportunity; I won't let it happen again. By the way I'm from Boston, not NJ!

Dave Martin on 11 March 2014

Time... And Time Again

Dear Peter,
Thanks for another excellent episode. I find it fascinating how the history keeps coming back to this problem of 'what is time'?

One thing struck me during this most recent episode: If time were not eternal, there must be difference between time and the units applicable to defining the extent of eternity. In our current reality, we are presumably experiencing the combined effects of both time and whatever medium contains eternity, but what was it like when only this eternity-filled medium existed (ie pre-time). Although this episode suggested several definitions of how 'time' exists and/or is perceived within a larger eternity, it's not evident that any of these philosophers adequately describe what there is when we have the medium for eternity to 'be' but no time to mark it out.

For example, with existence in such a timeless state, can anything change and can there be causality? It seems to me that for something to change, it not only has to have two states that are different, but also some separation between those states (usually that separation is 'time' for us). Without separation, the states simply coexist, and if they coexist, they are one and there is no possibility of change. For example, if I have a blue doorknob and then at some later time paint it red, there is change, but if I try to make it red and blue at the same time, it will always be unchangingly purple.

The nature of causality would have a similar problem, because causality requires change.

If causality breaks down in an existence in which time is not eternal, then a lot of other things would fall apart. For example, going back a good few episodes, Avicenna's proof of a necessary existent also breaks down, since it relies on axioms about the nature of causality to prove that a non- contingent existent must exist. In fact, if the nature of causality is not eternal, any pre-time creation cannot be ascribed to an agent, and we cannot know whether creation of the first contingent things actually needed an agent or not.

Further, if change is impossible without time, then time ( along with anything else) cannot be created, so it would seem that it must therefore be eternal.

Regards, Dave M

In reply to by Dave Martin

Peter Adamson on 12 March 2014

Time, eternity and causation

Right, there is a whole cluster of problems here, and one big one as you mention is that it is not so obvious how A can be the caus of B without any temporal relations (at a minimum you might think B has to first not exist, then exist, in order to be caused). I think that Avicenna pretty much solves this with the essence existence distinction: if the essence is contingent whatever makes it exist is its cause and that can happen either eternally or with a temporal beginning. But people like al-Kindi would not agree: he makes "created" and "eternal" mutually exclusive.

And then another issue you raise here is what to say about the "time" before time would exist. This isn't necessarily absurd: you can have two types of time, one which is eternally elapsing, the other tied to the phenomena that are occurring once, say, the universe is created. This is Razi's view, and one that Crescas at least entertains. We'll find it again soon in Abu l-Barakat al-Baghdadi. However the usual move would be to say that God is in timeless eternity and that time simply begins when he wants it to, so there is no "temporal" extension prior to God's creative act.

In reply to by Peter Adamson

Dave Martin on 12 March 2014

Time, Eternity and all that

Hi Peter,
Thanks for your response. There's a few things here for me to think about.

I see the Avicenna solution to causality, but I'm not sure it's truly satisfying. The only 'causality' we ever experience is marked by a temporal extension. Even when you take something like, say, gravity that seems to be there all the time and holds planets in orbit, it can be seen to be causal because of the temporal changes caused on the motion of the planet. It's not clear to me that an 'eternal causality' (something that perpetually holds some other thing in existence) is the same phenomenon or that it would follow the same rules as causality we experience in a temporal reality. For example, how do we know that contingent things needed a 'cause' before the existence of time (in our temporal reality, they only need a cause to flip them from nonexistent to existent; in the pre-temporal reality, there can be no flipping, so do things that exist before time need a cause)? Indeed, how are the caused things differentiated from the things causing them in a motionless timeless reality?

I accept what you say about the possibility of two types of time, but - if there are indeed two types - we live in a reality where both types are elapsing. It's not clear that any of the axioms or logic we are using to do 'philosophy' would hold in that part of reality in which only one of the two were operating. (Another way of looking at this is to say that if there are two types of time, there must be two types of causality and we shouldn't asume we know how the second type works, or - in Avicenna's case- use it to prove the existence of God.)

In reply to by Dave Martin

Peter Adamson on 12 March 2014

More on time

Yes, I agree both those points are a worry. With regard to the first what we need to do is make a case that causal dependence is possible without temporal sequence. Actually Avicenna's theory can be taken to mean that a cause is ALWAYS simultaneous with its effect: the cause is responsible for the effect's continued existence for as long as it goes on. On that view temporal sequence has nothing to do with causation at all! But that isn't an argument, only a way of looking at things that may not convince you. Gazali mentions an example that was offered by "the philosophers" of a finger eternally stirring water: no one would be confused about which is cause and which effect. Augustine gives a nice similar example of a foot eternally making a footprint in sand. What we need in any case is the idea of asymmetry without the idea of literal precedence.

Regarding the second point, you are right that there's an epistemic puzzle here: how do we know about this other kind of time which idein dependent of things we experience? Razi and Baghdadi both anticipate this and claim that time is immediately intelligible to us without needing motion as a prompt. This is something in the direction of the Kantian idea that time is just a condition of our experience rather than something we extract from experience. More on this in the episode on Baghdadi.

In reply to by Peter Adamson

Dave Martin on 12 March 2014

More on time

Thanks Peter
I'll look forward to the episode on Baghdadi.

I can't agree with Gazali and Augustine though. There is no way of knowing if the finger is moving the water or vice versa without applying knowledge gained from previous experiment. Similarly, you couldn't know whether the foot is making the impression or whether the formation of the impression was lowering the foot, without some preexisting knowledge about the nature of gravity. Therefore the idea of having 'no doubt' when doing either action 'eternally' is moot.

By the way, I don't think modern Physics has a comprehensive idea about what time is either, other than its passage seems to be associated with the direction of increasing chaos in the universe.

In reply to by Peter Adamson

Xavier on 9 February 2023

Non-temoral causation

Joining the above conversation very late.


Augustine, at some point in the Confession, maybe when he's discussing "in the beginning" suggests that an example of atemporal priority is like how song is the ordering of sound ad yet neither exist at different times to each other.


Do you think that this works as an example of non-temoral causation?

In reply to by Xavier

Peter Adamson on 10 February 2023

Non-temporal causation

Yes I like that. A nice example in Ghazali is that a finger stirring water is simultaneous with its effect; I think it is Augustine who has one about a foot causing a footprint while standing in sand. 

Xaratustra on 17 August 2016


Hi Peter,

I am not quite following the discussion about time. Things out there in the nature take time to happen, i.e. basically exchange energy. Even the whole universe, which is the home to time (and space) takes time to expand. The relation between time and energy is one of the most remarkable achievements of the 20th century by the lady physicists Emmy Noether in 1918.

Any phenomenon from planetary movements to chemical reactions in our body to seasonal behaviour of animals could in principle be used as a clock for time keeping, according to which other phenomena could be measured (of course the more accurate the scale, the more precise the time keeping is, for example by using an atomic clock).

This still remains unaffected by the modern (relativistic) physics, where one talks about "proper time". For instance if Hiawatha needs equivalent of 460 days (e.g. measured in units of a precise clock) to give birth to baby giraffe "Diantha", she would still need that amount of time even if she would be travelling past us in a spaceship with near-light speed, carrying a similar clock with her. Only our impression of time here on Earth would be different.

In fact, while floating in the mid-air, subtracting 100% physical interactions, there is no way for Avicenna to grasp the passage of time, unless he's hit by at least two migrating birds. It is his time-independent intellect though that says: ouch!

Apart from modern explanations, I wonder how did philosophers ever come to the conclusion that time could exist only in our minds?

In reply to by Xaratustra

Peter Adamson on 19 August 2016

Subjectivist views of time

Wow, that comment raises a lot of issues; obviously the modern way of thinking you discuss here has numerous different presuppositions that ancient and medieval thinkers did not share, including the idea that any motion could arbitrarily be made a clock (usually, they felt pressure to have some one universal time, often tied somehow to the motion of the cosmos). Regarding the last bit, Aristotle's definition of time as a measure of motion clearly invites subjectivist ("only in the mind") accounts of time, because it seems that a measurement happens only when someone measures, which sounds like a mental process. Augustine gives some other reasons for a subjectivist kind of view, which I discuss in episode 110.

In reply to by Peter Adamson

Xaratustra on 24 August 2016

Subjective account

Giving it a further thought, it seems that it might be possible to allow for an almost subjectivist account of time and still go strong with physics.

Physics tells us that we have to wait until something has happened (no matter relativistic or classical), e.g. exchange of energy or its conversion from one form to another. By choosing another phenomenon, we can quantify the "waiting" for the former by counting the number of occurrings of the latter. For example by experience you know that boiling an egg takes a bit longer than making two cups coffee in a row.

Put in other words, it is not the time that is passing, it is the physical phenomena that happen, but not instantly (regardless of any observer waiting for it or not). Assuming they either do happen instantly, or not at all, then there could be no waiting, and hence no feeling for time.

So time is more like a meta-concept that every body agrees on and makes the everyday life easier, much similar to paper money which is used by
everyone, instead of really trading goods with goods.

Therefore, in this sense, time for itself does not exist. It is just a concept in the mind!

I hope this definition can make the most subjectivist of philosophers happy.



SocraticPlato on 23 February 2022

Crescas, Augustine and time

Hi, nice episode as always!

I was wondering if there's any difference between Crescas's conception of time and that of Augustine.


In reply to by SocraticPlato

Peter Adamson on 23 February 2022

Augustine and Crescas

Ah, that's a nice question: both of them seem to be some sort of subjectivists about time and say it is dependent on the soul. So definitely comparable. If there is a difference it might be that Crescas is more within the debate over Aristotle's conception of time. So, if I understand him rightly, he is saying "sure there are measurable changes and motions out in the world but time only comes in when we count/measure them." Whereas Augustine's discussion in the Confessions offers a deeper exploration of how we experience time, because it is more about memory and expectation. Still I think as far as the metaphysics of time goes, they pretty much have the same view.

Xavier on 9 February 2023

Crescas anti-rationalist?

How come you and Tamara both described Crescas as ati-rationalist?


It seemed to me like he was engaging in rational work and was only being anti-Aristotle.


While I'm at it, what exactly separates the philosopher and the theologian? How come the Mu'tazilites are described as theologians and not philosophers when they're doing their work like expounding negative theology or divine simplicity?

In reply to by Xavier

Peter Adamson on 10 February 2023

Crescas and Kalam

This was a long time ago, and I don't remember what Prof Rudavsky said; but looking back at the text of the scripts, I said it was "tempting" to describe Crescas as an anti-rationalist and then went on to say that this would be a mistake. Here is the passage: "It’s tempting to caricature Gersonides and Crescas, the two great thinkers of medieval Judaism after Maimonides, as standard-bearers for the rationalist and anti-rationalist paths open to Jews in this period. There may be something to that idea (it’s easy to remember, for one thing). Yet Gersonides, despite his enthusiasm for Averroes, was also a critic of the previous philosophical tradition, and Crescas structured his Light of the Lord in pretty much the same way as Gersonides structured his Wars of the Lord. Both proceed by listing classic arguments of philosophy and then passing judgment upon them." (That's from the book version, not sure if it is exactly the same as in the audio podcast.)

And as for kalam and philosophy, you are preaching to the choir on that one! I have been arguing in many places for years that kalam should be counted as a philosophical tradition which is why I included it in this series. See also for instance my online article here:


In reply to by Peter Adamson

Xavier on 10 February 2023

Aquinas and Averroes

Just read your article, well said. 

I was not warm towards Russell because of his dismissal of Aquinas as not really being a philosopher (and some very rude off hand comments relating to the wellbeing and treatment of children of large families in "Why I am not a Christian", but that was merely personal). I guess it'll need to be said that Russell was consistent though when it came to Aquinas and Averroes. He didn't like the religious philosophers of any stripe it seems!


His contemporary, Frederick Copleston, on the other hand quite liked the scholastics as philosophers but he also led me astray with the "no more after Avicenna because of Al Ghazali" line. I have his 11 part History of Philosophy, which I am sure I'll read eventually but I've only read vol 1 and 2 (1=Greek/Latin and 2=Medieval until the start of 14th C) and that was about 5 years ago. Although, if I recall rightly, Copleston criticizes Ghazali in a way similar to how Ockham, and sometimes Scotus (as with Pope Benedict XVI in the Regensburg lecture), are often critiqued in Catholic circles: For introducing voluntarism to theology. The problem with doing this, they say, is that it kills the validity of reason as a way to understand God. The extreme voluntarist would say that God can arbitrarily decide that 2 + 2 is 5 or that murder is virtuous. In the wake of this, reason and thus philosophy can not be regarded as ultimate guides to objective true and fade away.


I have only just started your later Eastern Islam episodes and I'm sure you'll probably disabuse me there anyway. But I wonder what you think about this old strain of thought.

1. Is Al Ghazali like a Muslim parallel to William of Ockham?

2. Does theological voluntarism cause problems for the project of doing philosophy?

3. Is Frederick Copleston's History of Philosophy a worthwhile series or do you think it has become irreparably dated?


Kind regards,

In reply to by Xavier

Peter Adamson on 10 February 2023

Ghazali etc

1. That's an interesting comparison; I guess I'd need to hear your reasoning there, the comparison who leaps to mind for me more is Fakhr al-Din al-Razi and Scotus.

2. Well, maybe. Voluntarism is often associated with limitations placed on reason, or even outright skepticism. But you can place even severe limits on reason and still leave plenty of room to do philosophy (e.g. about the nature of those limits, but also whatever doesn't stray beyond the limits). I think this is basically what we get in Asharite philosophical kalam and also in Protestant philosophy, cf. the current episodes that are coming out.

3. You know I own Copleston and read the series back in college or grad school, but I have deliberately avoided going through that or any other single-author general history of philosophy to avoid being unduly influenced (I looked at Russell not too long ago but figured that was safe since, like, I'm obviously not going to be taking an approach like his). So I would assume that Copleston must be quite outdated, but can't really give you confirmation. Obviously he wrote so long ago that a vast amount of research came after him, so only for that reason he would be quite out of date but it might still be worth consulting.

In reply to by Peter Adamson

Xavier on 11 February 2023

Many thanks and an apology to Copleston

Thanks for taking the time to reply and thank you for your entire project.


I really don't know enough to make a good case for seeing Al Ghazali and Ockham as having parallel effects on the philosophy of each of their religions other than they both were voluntarists and both set about critiquing the milestone Aristotelians before them like Avicenna and Aquinas.

I wonder if it would be true to say that, generally in the centuries that followed, in Islam the voluntarist critique was taken and Al Ghazali carries the day over Avicenna and in Catholicism the voluntarist critique was rejected in favour of Aquinas.


However, I am a blockhead who needs reprimanding. I just went and found my Copleston volume 2 to see what he had to say about Islamic philosophy and it isn't at all how I was recalling. I wonder who else I've listened to that I think of Al Ghazali as someone who weakened Islamic philosophy and concreted divine voluntarism. Anyway, Copleston devotes some 15 pages to the Islamic philosophers. He starts by explaining that Islamic philosophy has lots to it that is intrinsically interesting but that his intention is only write about philosophy in Medieval Christendom and so he only intends to give a brief sketch so that he can talk about its influence on Medieval Christendom. He then goes on to give a brief account of Alfarabi, Avicenna, and 'Algazel' as representing the Eastern Islamic thought and Averroes as representing the Western Islamic thought. He makes no mention whatever of any decline or end of philosophy in Islam! He only stops where he stops because that's far enough for him to start talking about Aquinas etc.

Furthermore, he makes no mention of voluntarism in Al Ghazali at all. He doesn't critique Al Ghazali at all, if anything the description is sympathetic.

So I would say that Copleston, happily, does not perpetuate the myth of the demise of Islamic philosophy in that book :)


By the way, I listened this morning to episode 177 about the Essence/Existence debates with Al Tusi and others. I was amazed at the parellels to Aquinas and Scotus. Al Tusi and Aquinas are nearly exact contemporaries. Could they have known of each other's works or are their sorts of talking points on existence/essence sort of inevitable in debates that are downstream from Avicenna in history?

In reply to by Xavier

Peter Adamson on 11 February 2023

Copleston and existence

Thanks, that's interesting about Copleston. As a Thomist he would have been more alive to the value of Avicenna etc than Russell was (Russell being famous for his dismissive remarks about philosophy in the Islamic world).


And yes, the similarities between Aquinas/Ghent/Scotus and Razi/Tusi are really striking, but I do think it is because both traditions are working out potential implications of Avicenna's philosophy. So what explains the parallel is the same starting point - this happens on other topics too and is one reason I always say that Avicenna is the most important medieval philosopher.  

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