Many sentences are relatively vague; others relatively precise. A term that is perfectly precise would generate no borderline cases, and although this is often presented as a theoretical ideal it is extremely unclear that any learnable, speakable language could begin to meet it. For even basic observations (‘this is red’) admit of borderline cases (in the oranges and purples), and even when care is taken to make terms as precise as possible, unforeseen contingencies, new kinds of discovery, and things with new combinations of properties, may always provide hard cases whose classification is left unclear. The best semantic treatment of vagueness is unsettled: issues include the correct way to resolve the Sorites paradox, and the question of whether classical logic should be modified to countenance degrees of truth, corresponding to degrees of vagueness. see also supervaluation.