Hi Sam,

Scholars and Classicists have been arguing over the correct interpretation of Parmenides argument for millennia so no worries about getting it straight-off. I'll try to give a brief break-down (let me know if get's confusing at any point).

To give the something like the standard text book interpretation of Parmenides let's look at him in the context of his predecessors, the Ionian cosmologists. That school, or at least the records of which that have come down to us, took as its central question what was the ultimate constituent of world, and typically answered with one of the four elements, or, in the case of Anaximander, something approaching indentity-less Prime Matter.
 
Parmenides made a radical ontological advance on all this speculation when he announced that what was common to all things was that they existed i.e. had being, and thus Being was the ultimate. As can be seen both the Ionians and Parmenides worked on a reductionist account which in the former’s case lead to a radical 'being' monism. There is only absolute being and non-being.
 
So his proof is something like:
 
1. Nothing can effect spontaneous change within itself
 
2. All that exists is one i.e being (the unified 'being' globule')
 
3. To be different from being is only non-being.
 
4, There for the only 'thing' which could affect change is non-being
 
5. But non-being is not a thing, it’s not any thing, and thus can do nothing.
 
6. Therefore there is no way for change to come about.
 
Aristotle and Plato gave a two stage elaboration of where Parmenides went wrong. For one thing he attempted to abolish all identity and with it all separate types of being – to make sense of these types Plato developed his famous theory of Forms which carve up the world and prevent it being a single ontological blob. Both philosophers took the mark of a ‘normal’ being not just that it existed, for of course common sense tells us that contra Parmenides somethings which do not exist could do so, but something that had an identity determining the type of being it was from all others. Identity was then taken parallel with knowability for ‘What cannot be cannot be known’ as Parmenides himself said. We shall return to this in a minute.
 
Aristotle also remarked that there were different senses of the word ‘being’, including ‘being-possible’, the crucial distinction Parmenides missed. This ‘being possible’ or more accurately having the capacity to go from one type of being into another e.g. from ball-shaped to disk-shaped, is what he termed potentiality.  So Parmenides would have been correct were he talking about a being which lacked any degree of potentiality.
 

sam regarf wrote:

It seems to me that if one rejects the notion of the "being" monism as you call it (which seems quite easy to do away with), then Parmenides question falls away and we are left without good reason for believeing in the distinction between act and potency.

Your parenthetical remark indicates the problem: is there a way ("easy" or otherwise) to do away with "being" monism that isn't equivalent to Aristotle's distinction between act and potency? Parmenides aside, Aristotle claims to be presenting an analysis of real (non-illusory) change, and it seems self-evident that such change really does occur. Is there some other, better analysis that doesn't in the end wind up saying essentially the same thing in different words?

Last edited by Scott (7/03/2015 12:29 pm)

ArmandoAlvarez wrote:

I don't see why change in general is a question that needs explaining at all, other than the nature of time. What seems to enable any change is time.  As far as I know, we don't really understand what time is, but act and potency don't help with that.
But I assume I'm just taking for granted some unquestioned assumption here.  That's natural in introductory philosophy.

Yes, and I think the unquestioned assumption is that "time" is something that "change" in some sense happens in. On the Aristotelian view (including Aristotelian Thomism), change comes ontologically first; time is just a measure of change. Time doesn't enable change; change enables time.

As for why change in general requires an explanation:

One reason is that in order for there to be genuine change, there must be something that undergoes, and "persists" through, the change; otherwise we have not "change" but mere replacement. The Socrates that goes from sitting to standing is the same Socrates before and after; he's not "replaced" by a brand-new Socrates when he stands up. And yet he was sitting and now is standing. So we need to explain how that's possible, and the act/potency distinction (in whatever language we express it) is the way Aristotle and his followers do it.

Another reason is that (as we know if we accept the act/potency analysis) any change involves a reduction of potency to act, and potencies, being mere potencies, can't reduce themselves to act. Thus anything that undergoes change must be changed by something already in act, and we need to explain how such a process can get started. (That's where the Prime Mover comes in.)

Last edited by Scott (7/12/2015 7:42 pm)

ArmandoAlvarez wrote:

How does this jive with the idea in modern physics that time is a dimension? 

I think it jibes just fine as long as we bear in mind that an abstract mathetical structure doesn't capture the whole reality it models. Generally speaking such models omit a lot of qualitative features, and in this instance the mathematical structure abstracts away (Aquinas would say "prescinds from") the very occurrence of change itself.

It's not therefore wrong, because if God eternally knows all such moments in their full presentness there must be a sense in which such moments can legitimately be treated as "all there at once." But it also can't be that simple, because the model doesn't (and isn't intended to) capture that "presentness" or the "movement" from one "present" to another. In short, it's not intended to be a model of change in the first place -- only of serial order, which for modelling purposes it treats as spatial rather than temporal (when in reality it might e.g. be both).