This is a common "problem" cited in analytic philosophy, the whole "this sentence is false" thing. I was writing about this in my topic about the idiocy of analytic philosophy; the Crete paradox, which isn't a paradox at all, of "All Cretans are liars" when the speaker is himself of Crete. What it shows is that humans operate linguistically in a kind of gray area ambiguity of not understanding what they are doing or why. Language affords this gray middle space of partial unknown, a kind of surrogate and externalized partial unconsciousness. This is a good feature of language that it allows for this, and the analytics think of it only as an error and problem because these analytic thinkers are idolizing computer robot consciousness, they are all trying very hard not to be human. So naturally "human vagueness" is a problem for them, even though the vagueness in this and many other cases is a productive and healthful one.
Real problem: you are nature, so how do you get a species of somewhat becoming-self-conscious apes to externalize their unconsciousness? If it is externalized directly it is simply non-conscious instinct as all animals already have, but if it becomes more conscious then it becomes not-unconscious.
Answer: nature decides to invent a higher form of language. Humans evolved the capacity not only for very dexterous tongues, mouths, lips and vocal chords but also the key ability in the brain matter to emulate the position of all those parts an instant before they arrive at that position. This allowed these human apes to really diversify and solidify a large number of very specific morphemes of speech-utterances, the vowel and consonant sounds that we call the alphabet. This introduces an intermediary between the instinctive unconscious excess-force and the utterance itself; now this utterance is able to distance itself (differentiate as you said Fixed) from the unconsciousness excess energy of psyche and body from which the utterances actually are always coming. Every vocal utterance is (and this is still true today of humans) a kind of pressure-release of some inner unconscious and instinctive excess. Speech deep down is the mouthpiece of the unconscious. But with this middle-space now mediating the end result formation of the utterances there naturally arises a backward pressure upon the unconscious which pressure begins to retroactively organize that unconscious from which an utterance came. Hence humans learned about what we call reason.
Examples like "this sentence is false" are categorical errors of falsely conflating one thing with another. "All Cretans are liars, I am a Cretan, therefore I am a liar, therefore when I said all Cretans are liars I must have been lying, therefore all Cretans are not liars, therefore whati said is true, therefore all Cretans are liars..." this sort of thing is idiotic. It's like a human mind degenerating into a little closed loop in a programming code. We don't work like that, neither does language, neither does Reason, neither does meaning, neither does the unconscious. These examples only illustrate that philosophers don't yet understand what language is and what it means when we use language to communicate something. Each of these "paradoxes" that false philosophers use to mystify college students in Phil 101 courses while stealing those kids money in the process, each such "paradox" breaks down completely upon closer examination.
Analytic philosophy is the enemy.
"The highest-order danger is articulated speech." --Jordan Peterson
Aw Shit, https://m.youtube.com/watch?v=RIW59yai0_I
"I count him braver who overcomes his desires than him who conquers his enemies; for the hardest victory is over self." --Aristotle