Not-Being in Sophist

The following is an attempt to explore all the different meanings of "is" and "be" that I have seen scholars talk about or thought of in reading Plato.
The following is a mess: some of these things work in English, some don't, and some work easily in Greek, while some don't.
Also, the "is" discussed here is a single verb in Greek and a single verb in English, BUT there are synonyms that work for some of these meanings, both in Greek and English.
So this is not entirely about English or Greek or what these things refer to or how the words are used in sentences.
It's a mess, a mash-up. But a good one, one that should show us how big the problems are that underlie using simple little words we hardly ever think about.

1. 'X is Y' can mean:
1. X and Y are identical: they are completely the same thing. 'This triangle is the triangle I am referring to.'
   
2. X and Y are a member of a set and a set: 'this obstuse triangle is a triangle.'
3. Y is a predicate of X: Y applies accurately to X as a quality/quantity, etc.: 'This thing is red.' 'This thing is twofold.'
1. NOTE: 1.2 and 1.3 may be the same: it perhaps depends if you think it makes a difference when Y is a noun v. an adjective: or perhaps it depends on the sort of thing Y refers to: you might think that such sentences involve X's that are natural kinds, whereas the Y's are everything else.
   
2. and then there is the difference:
   
1. X is Y in its own right, by itself: let's call this requiring two things
   
1. The horse is an equine (regardless of anything other than the horse: all we need is the horse and whatever 'being' the word 'is' means)
   
2. X is Y in a way that requires other things: let's call this requiring > 2 things.
   
1. The horse is my father's. (which requires a horse and me and my father and something like what 'is' refers to, perhaps a 'belonging' relation)
• Note that this difference is a different kind of difference from those in 1.1-1.3 above.
  
3. A whole new set of different meanings of "be": "X is" can mean:
1. X is.= X exists. which we could redo as 'X isEP.' This means that X exists physically. Only physical, spatio-temporal things can be X.
   
2. X is.= X is a form. which we could redo as 'X isEF.' This means that x exists in that permanent unchanging way that Forms do. Only forms can be X.
3. X is.= X is true. which we could redo as 'X isT.' This means that X is true.
4. X is.= X is good. which we could redo as 'X isG.' This means that X is good.
   
5. X is.=X is real. which we could redo as X isR. This means that X is among the things we think are 'real' (for Plato, probably, all physically existent things are real, but there are also other (more) real things, Forms)
6. X is.=X is some thing. Which we could redo as X is a thing, one of the set of things we call things (includes physical things, Forms, and fictional things, figments of imagination, and maybe even things that don't exist and no one has even thought of, and maybe even nonsense, etc.)
• Note that ALL of these can be changed to "X is Y" if Y is "a physically existent thing" or "a Form" or "real" or "a thing" or in the form "X ___-ly is Y" if ____-ly is "really" or "Formally" or phrased  in more complex adverbial ways (e.g. "X is Y, in the way that anything you could ever think of is a thing, even if you don't ever think of it").
  

• Note that Plato rarely distinguish these meanings, and several verbs can indicate them, and also that adjectives and adverbs can be used to distinguish them:
• But distinguishing them for him is essential to making his arguments work at all and therefore to getting any juice out of various passages we have read in Tht., Rep., Parm., Soph., etc.
• We may have to reword some of them: X is Y can mean that X partakes of the Form y.

• And then there is a difference that is hard to recreate in English, but clearly works in Greek: To prepare us to understand that difference, consider the verb 'teach' in the following:
1. Jacques teaches.
2. Jacques teaches Latin.
3. Jacques still teaches, but doesn't teach Latin.
1. Jacques still teaches, but doesn't teach Latin. He teaches Greek.
   
• Note that in 1, teaching is considered a complete verb: you might ask "what does he teach," but you don't have to: it is considered a complete thought by itself.
• Note that in 2, the use of the verb 'teach' has an object, what Jacques teaches. That sentence too is considered a complete thought by itself.
  
• COMPARE THAT TO:
  
1. Jacques is growing.
2. Jacques is growing trees.
• In 1, it makes no sense to ask "what is Jacques growing": it just means that Jacques is growing, not that he is growing something.
• But in 2, we need to know what he is growing to complete the sentence.
  
• So we have two very different uses of "growing"
• NOW, I am going to tell you, because it's true, that Greek arguably uses "is" in the same way as we saw 'grow' used, but also that it might use it in the way that we say 'teach' used: it's just not completely clear. The only way to tell is to read the Greek of each passage and think hard about what it must/can mean. And you have to do that a lot in Plato.