"One suffering may be so wholly incommensurable with another that no true impression is given by calling it a hundred or a thousand times greater; in other words, the lesser, endured in a thousand frames, could not for an instant be set against the greater endured in a single frame. Nor is the essential distinction between endurable and unendurable pain at all impugned, as some seem to think, by the impossibility of drawing a distinct line between them — an argument which would equally forbid us to call yellow and red essentially distinct colours."