One of the first things that people noticed when they started thinking about 
language as language was that words tend to fall into categories and that the 
members of these categories behave in similar ways.What allows us to say that shove in sentence (1) functions as a noun, but shoved in 
sentence (2) functions as a verb?The meaning of both sentences, after all, is 
essentially the same.And how do we account for verbs like hear or undergo?In a 
sentence like
(3) Jessica underwent a surgery to remove the tonsils as a child.Consider sentences such as
(1) John gave him a shove.(2) John shoved him.