Matt how do you see this relating to the way Epicurus analyzed the question. My gut reaction is that what you are describing is such high-level logic, based so strongly on the word definitions without any connections with observations in "this" world, that Epicurus would not recommend relying on such an argument. I could be wrong, but this might be a good example to show that Epicurean logic as described in Lucretius and Philodemus always starts with that which is observable and rests primarily on what we do and do not observe. However I may be misunderstanding the Parmenides position.
It's in this respect that I strongly agree with what I think is or what I think should be Elayne's main point -- that use of "pure logic" as a reasonable grounds for making big conclusions is to be ruled out as an acceptable method. In fact I might say that it sounds like Parmenides's argument would suffer from the same problems as we are discussing to be the problem with hypotheticals and abstractions in the first place -- there are too many assumptions being made for someone who is grounded in the evidence of the senses to have confidence in the result.
We simply cannot argue the opposite of this concept because it’s impossible.
1. I wonder if the Epicureans would use the word "inconceivable" rather than "impossible."
2. I wonder if the meaning of both of the words "impossible" and "inconceivable" would be discussed as part of a program of Epicurean instruction.
3. I wonder if, absent some form of "logic from first principles" it is even possible to use words like "impossible" or "inconceivable" in an understandable manner.
4. I wonder if the need to label things as "possible/impossible" or "conceivable/inconceivable" would be an argument why an "observation is everything" approach might not be considered as a sufficient philosophy of life by Epicurus. (Or maybe he would say it would be OK - Frances Wright was willing to put essentially those words in his mouth ).
Matt this discussion takes me back to another passage of "A Few Days In Athens" I always questioned, from Chapter 14. where Wright has Epicurus say:
To deny the existence of the gods would indeed be presumption in a philosopher; a presumption equaled only by that of him who should assert their existence.”
“How!” exclaimed the youth, with a countenance in which astonishment seemed to suspend every other expression.
“As I never saw the gods, my son,” calmly continued the Sage, “I cannot assert their existence; and, that I never saw them, is no reason for my denying it.”
“But do we believe nothing except that of which we have ocular demonstration?”
“Nothing, at least, for which we have not the evidence of one or more of our senses; that is, when we believe on just grounds, which, I grant, taking men collectively, is very seldom.”
First, I don't think this accurately reflects Epicurus' position at all, and it seems mighty presumptuous to me that Wright put these words in Epicurus' mouth. But, having got that observation out of the way, we should ask:
What should WE think of this? Is it correct? Is it the position we should take today? How does it fit with Epicurus' and Parmenides' arguments?
Matt (or anyone) separate and apart from Parmenides, what do you think about these questions?
2. I wonder if the meaning of both of the words "impossible" and "inconceivable" would be discussed as part of a program of Epicurean instruction.
3. I wonder if, absent some form of "logic from first principles" it is even possible to use words like "impossible" or "inconceivable" in an understandable manner.
4. I wonder if the need to label things as "possible/impossible" or "conceivable/inconceivable" would be an argument why an "observation is everything" approach might not be considered as a sufficient philosophy of life by Epicurus. (Or maybe he would say it would be OK - Frances Wright was willing to put essentially those words in his mouth ).
Remember the forum is "asynchronus" -- I am being called away to "real world" work right now myself!
"Observation is everything" is the position of a type of skeptic, who does not want to form a workable and understandable mental model of how nature works. We are far closer to "everything we think we base on observation, and we infer by analogy from this empirical basis in order to conceive that which cannot be observed."
Hi friends. Hello Bryan. There is an anecdotal story of what people were thinking about the Ionian natural philosophers, as also they called, by adacemics, pre-socratics.
As an exaggeration, people said that those philosophers were famous to observe and hearing even the coolness dripping on a leaf, and after their observations they drew some of their own conclusions.
There is an anecdotal story with Democritus that will make Matt to smile. 
One morning, they say, Democritus met a girl that she lived in his neighborhood, so he greeted her, saying:
- Good morning Girl.
One night, the same girl, had intercourse with a man.
And when Democritus met her the next morning, he kindly greeted her saying:
- Good morning woman. 
Hello Elli, yes that is right on topic, very amusing, and new to me! Thank you.
No, please do not mention anything about Parmenides to Elayne, she will be upset and we will confront and some other troubles. Parmenides was the great fiesta of idealists Plato and Socrates. All of their thoughts were inspired from him. Parmenids is against Epicurus, and sometimes some persons confuse Epicurus ideas with him. Parmenides conclusions are against to the manifold way of epicurean canon the swerve and the experiences that are testified by our senses and feelings.
Since Parmenides said this : All reality is one thing, change is impossible, and existence is timeless, uniform, and necessary. In the way to form an opinion, he explains the world of appearances, in which one's sensory faculties lead to conceptions which are false and deceitful. 
No, please do not mention anything about Parmenides to Elayne, she will be upset and we will confront and some other troubles. Parmenides was the great fiesta of idealists Plato and Socrates.
Sounds like all of us, and not just Elayne would line up against Parmenides. The trick would be articulating exactly WHY and WhERE we think he went wrong.
Tentatively I would say that we should apply the same analysis - that it is not Paermenides use of logic in general, but his specific application of logic and reasoning to the problem, in that he failed to ground his initial premises sufficiently in the observation of the senses, and to tie the steps in his chain or reasoning to reality verifiable through the senses.
But since I've yet to really figure out Parmenides' chain of reasoning , or his conclusions either, I can't say even that with confidence. If one of his conclusions was "motion is impossible" then we can attack that with confidence, but I can't get a fix on what his other conclusions were all about.
"Observation is everything" is the position of a type of skeptic, who does not want to form a workable and understandable mental model of how nature works.
Bryan put "observation is everything" in quotes, and I do think that is a very fair summary of the Wright position. But since I want to be rigorously fair in the assertion (again I agree with Bryan) that this amounts to a form of skepticism. That's a serious charge, and anyone evaluating whether it is justified ought to consider this passage from Chapter 15 of A Few Days in Athens. There is more in her later "Course of Popular Lectures" but since these are the words she places in the voice of Leontium as representing core Epicurean doctrine, this deserves special scrutiny.
You have heard of, and studied various systems of philosophy; but real philosophy is opposed to all systems. Her whole business is observation; and the results of that observation constitute all her knowledge. She receives no truths, until she has tested them by experience; she advances no opinions, unsupported by the testimony of facts; she acknowledges no virtue, but that involved in beneficial actions; no vice, but that involved in actions hurtful to ourselves or to others. Above all, she advances no dogmas, — is slow to assert what is, — and calls nothing impossible. The science of philosophy is simply a science of observation, both as regards the world without us, and the world within; and, to advance in it, are requisite only sound senses, well developed and exercised faculties, and a mind free of prejudice. The objects she has in view, as regards the external world, are, first, to see things as they are, and secondly, to examine their structure, to ascertain their properties, and to observe their relations one to the other. — As respects the world within, or the philosophy of mind, she has in view, first, to examine our sensations, or the impressions of external things on our senses; which operation involves, and is involved in, the examination of those external things themselves: secondly, to trace back to our sensations, the first development of all our faculties; and again, from these sensations, and the exercise of our different faculties as developed by them, to trace the gradual formation of our moral feelings, and of all our other emotions: thirdly, to analyze all these our sensations, thoughts, and emotions, — that is, to examine the qualities of our own internal, sentient matter, with the same, and yet more, closeness of scrutiny, than we have applied to the examination of the matter that is without us finally, to investigate the justness of our moral feelings, and to weigh the merit and demerit of human actions; which is, in other words, to judge of their tendency to produce good or evil, — to excite pleasurable or painful feelings in ourselves or others. You will observe, therefore, that, both as regards the philosophy of physics, and the philosophy of mind, all is simply a process of investigation. It is a journey of discovery, in which, in the one case, we commission our senses to examine the qualities of that matter, which is around us, and, in the other, endeavor, by attention to the varieties of our consciousness, to gain a knowledge of those qualities of matter which constitute our susceptibilities of thought and feeling.”
