The trouble with non-quantifiable terms is that said terms are used in a wide variety of areas so they acquire different connotations and as such are "soft" words. One such term is the word "proposition." In Logic it is loosely synonymous with the word statement. E.g "The A-proposition is a Universal Affirmative "proposition" or statement; All humans are mortal beings. Christian Goldbach's statement about "prime #'s has been called his "Theorem." The term "proposition" does imply, indeed, a theory which is rather "tentative" than one we could rightly called "theorem."