166 - Tamar Rudavsky on Gersonides and Crescas

Posted on 9 March 2014

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 9 March 2014

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

Maciek Zajac 9 March 2014

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?

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).

Tom Roche 10 March 2014

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" :-)

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 10 March 2014

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

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.

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.)

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.

Dave Martin 12 March 2014

In reply to by Peter Adamson

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.

Xaratustra 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?

Peter Adamson 19 August 2016

In reply to by Xaratustra

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.

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 23 February 2022

Hi, nice episode as always!

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


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.

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