Here is my answer to the questions I raised yesterday.
Irwin begins by agreeing (it seems) that, for Plato, Flux implies Compresence (as I have maintained, on the 'simple' interpretation):
These appearances of compresence are the result of motion, change, and mingling, so that everything merely comes to be (hard, soft, light, heavy, and so on) and nothing stably is what we take it to be (Tht. 152d2-e1).But then he shifts and says that for Plato the implication actually works in the other way, viz. that Compresence implies Flux, because when opposites are compresent in a thing they make it unstable:
In speaking of heavy, light, and so on, Plato clearly refers to the Heracleitean doctrine of the compresence of opposites; he thinks no further explanation is needed to justify him in describing such a doctrine as a doctrine of flux. He therefore assumes that it is appropriate to speak of 'flux', 'change', and 'becoming' in describing the instability that is manifested in the compresence of opposites.So how is it that Irwin so easily converts "A implies B" into "B implies A"? Does Plato think that Flux implies Compresence (as the text seems to say, and as the 'simple' interpretation asserts) or that Compresence implies Flux (as Irwin construe him as saying)?
The reason for this shift in interpretation, is that Irwin interprets flux, and change, as mere 'succession' in time of properties: for something to be in flux is for it to have (stably and completely) some property F at one time and (stably and completely) the property not-F at some other time. On this view, Flux couldn't possibly imply Compresence, and, if that is how one understood flux or change, the most charitable interpretation one could place on Plato would be to hold that he thinks Compresence suggests or implies Flux, perhaps because Flux in some broad and extended sense includes Compresence. So "A implies B" gets converted to "B implies A" by charity!
That Irwin interprets Flux as the succession of properties over time:
In Plato's report, 'Heracleitus says somewhere that everything passes away and nothing remains, and in likening beings to the flow of a river he says that you could not step into the same river twice' (Cra. 402a8-10). This claim is about the succession of properties in the same subject over time.(Notice that this interpretation of the 'river fragment' in Plato requires that we think Plato thought nothing of "we step and do not step; we both are and are not", and also that Plato failed to read "Everything passes away and nothing remains" in the subtle way suggested by Catherine Osborne in a comment on this blog.)
That any view about Flux as the succession of properties over time could imply nothing about Compresence:
Plato does not assume that the instability Protagoras attributes to things is simply change over time; he uses terms that are appropriate for change in order to describe the instability involved in the compresence of opposites.Two points in conclusion:
We ought not to assume, then, that when Plato speaks of flux he must have succession in mind; and so we ought not to be surprised when he begins by speaking of compresence and continues by speaking of change. ...
If Aristotle see that this is Plato's conception of flux, he does not mean to say that Plato thinks sensible objects undergo continual change over time, or that change over time is what makes them unsuitable as objects of knowledge. He may simply recognize that, given Plato's broad interpretation of flux, compresence of opposites counts as a kind of flux. We ought not to conclude, then, that Plato's argument from flux in sensibles relies on anything more than the compresence of opposites.
1. Irwin in effect argues: "For Plato, Flux boils down to Compresence. Thus, everything he wants to say about Flux is captured already in my account of Compresence." But this won't work, because the doctrine of Flux for Plato is a doctrine about the change of sensible particulars. Even Irwin uses this language, e.g. "sensible objects undergo continual change over time" (see immediately above). So if Flux boiled down to Compresence, this would be the simultaneous compresence of opposite properties in sensible objects, not the loose compresence of opposite properties, in Irwin's sense (as explained in earlier posts). Admit that Flux boils down to Compresence, and one is still stuck with two doctrines of Compresence in Plato.
2. Whether Irwin's view of Compresence of Opposites is in the end a philosophically more sophisticated view than what I have called the 'simple' view, depends upon the sophistication of (i) Irwin's compresence of properties; and (ii) the interpretation of change as mere succession of properties over time.
And we may leave it at that.