“If a body constantly changed its weight, it would make nonsense to talk about ‘its weight’”, “If the chair behaved in this manner, we wouldn't talk about ‘a chair’”.
  “If the natural colour only lasted for half an hour, it would loose its point to talk about the ‘natural colour’ of an object.”
  Certain expressions have their sense in a certain behaviour being the rule & not the exception.
  The imporance of these remarks: that it often seems as though grammar said something about objects, whereas it treats of samples. But isn't it in the nature of the world that there is such an object as blue? Isn't it in the nature … that there is a foot, a unit, etc.?