Chapter 2 contains an interesting excursus on how apparently clearcut notions such as 'species' become more indeterminate on closer inspection, and Chapter 3 points out that attempts to turn vague terms such as obesity, poverty, and intelligence into precisely defined notions suitable for scientific investigation are subject to arbitrariness and residual vagueness.
if the light is bright at step n, then tolerance dictates that it will also be bright at step n + 1.