A little further on in Russell's History of Western Philosophy, and Plato's examination and perceived refutation of universal flux is examined and criticised by Russell, though whatever their attitudes to universal flux or lack of is not the issue here but instead what is of interest is a point within their time-stretched dialogue where is written:
Plato gets his results by applying to processes of continuous change such logical oppositions as perceiving and not-perceiving, knowing and not-knowing.
Russell describes the process of a person disappearing from view when viewed and finally not viewed in fog as a gradual process and so the logical opposites of perceiving and not-perceiving nothing like as clearly demarcated and fixed as Plato likes to assume. However, whatever they're getting worked up about is not the point here, and what I would like instead to look at is this notion of logical opposites, which may then put in focus the broader investigation as a sensible, or not, dynamic of language.
An opposite in a pure 'logical' sense is where two opposing entities perfectly balance each other out, or negate each other, leading, where the two come in contact, to a state where neither exists. Thus minus two is the opposite to plus two, and their set in motion against one another results in nought. They perfectly oppose each other; are logical opposites, i.e. are on precisely opposite sides from a definite point of demarcation, here being zero. Minus two does not exist however in reality outside of such language forms - linguistic or mathematical. You can have two of something, lets say shoes, but you cannot have minus two shoes. It's a senseless notion. So there are no opposites in a numerical descriptive sense in the world of ordinary reality.
Another notion of opposition might be black and white, but logical opposites negate each other, leading to nought or non-existence, whereas black and white coming in contact result not in nothing but grey. So they are not opposites, but simply different. Similarly, and more obviously, fat is not opposite to thin. Whether it's even meaningful to even talk of fat and thin coming into contact in the form of a kind of experimental equation is very doubtful, but even if it is permitted, this 'conflict of opposites' of fat and thin does not yield nought or the negation of the two, but something else altogether, if indeed anything. So again these are not opposites, and the same with tall and short, happy and sad, and so on. These are different, perhaps substantially different but not opposites.
And then the notion of perceiving and not-perceiving that Russell and Plato consider such logical opposites, from which acceptance they proceed with their discussion across the ages as to flux or not. I am now looking at a wall and the many other things within that visual field. It makes no sense to talk of an opposite to such experience, and the alleged logical opposition of not-seeing isn't something which occurs. There is no such phenomenon as not seeing something, or not eating, not running, etc. This is merely words without reference to anything. And also as in the mathematical example, the interaction of two logical opposites leads to nought, whereas this not-perceiving is already nought; and nought interacting with a positive does not produce nought. Instead the positive remains as it is. And since this notion of not-perceiving is nothing, a non-event, how can it be meaningful to talk of anything interacting with nothing? There is nothing to interact with. No interaction occurs.
The only sense in which it is meaningful to talk of logical opposites is in mathematics. And so whereas Plato and Russell imagine that they are having a genuine intellectual investigation of some real issue, their words instead refer to nothing; their discussion, as a dynamic of language which is of course what it can only be, doesn't actually exist as it's without meaning, and logical language without meaning is simply an unreal illusion.
I am very threadbare in my knowledge of the following, but the very notion of a conflict of opposites as a creative force, such as seems to be a notion of Hegel's, is nonsensical, as there are no such opposites apart from within mathematics, and even within mathematics where the opposites meet, the conflict or union of these opposites results not in some creative new synthesis but simply nought.