The crow example is meant to be absurd and point to the fact that science a. attempts to categorize the complex world and b. our language is inadequate. Rather than saying All crows are black based on a slice of experience and based on the various ways we see the world. ..we should say "It seems to ME AT THIS POINT IN TIME that all crows are black". Maybe crows were brown 3000 years ago. Maybe they're evolving to another color 3000 from now. Maybe my perception of black and YOUR perception of black are different. A little modesty is all that is asked for.