As far as I was taught and read in various places (examples: 1, 2), some adjectives in English are not comparable, which is that they don't have comparative and superlative forms. Why is that? I think that every adjective can be compared.
I will use these adjectives commonly considered noncomparable as examples: “unique” and “triangular”. The idea is that everything ‹x› is more ‹x› than everything not ‹x› for all adjectives ‹x›.
Everything unique is more unique than everything not unique, and everything unique is most unique because there can't be anything more unique than unique. Example: “The Night Watch is more unique than every one of the paintings of Golden Gate Bridge.” (So The Night Watch is unique, and the paintings of Golden Gate Bridge are not unique.)
Similarly, everything triangular is more triangular than everything not triangular and so on. Example: “Every triangle is more triangular than every square.”
This question isn't about grading. I consider that these adjectives are binary, so everything is either that or not that. Grading words like “very” and “quite” don't do anything. With “unique”, that could be debated because “unique” could mean “very special”, but I can't imagine that anything is not completely triangular or not triangular in the world of polygons. My idea is that, the words are not (sensibly) gradable, but comparing them makes sense.