Although something that is illegible is certainly unreadable, you have hit here on the fact that the converse is false, explaining why we need both words. (I.e.: a piece of writing is illegible if the glyphs that constitute it cannot be discovered; the unfortunate comment you found was made only of recognisable glyphs, so perfectly legible, but unreadable.)
Although something that is illegible is certainly unreadable, you have hit here on the fact that the converse is false, explaining why we need both words. (I.e.: a piece of writing is illegible if the glyphs that constitute it cannot be discovered; the unfortunate comment you found was made only of recognisable glyphs, so perfectly legible, but unreadable.)