a good puzzle

my dad is a teacher. last night, he was grading papers, and i read one of them.
the assignment was to write about a misunderstanding or an argument. one boy, the one whose paper i read, wrote a paper on an argument he had with his friend about opposites.
his friends said that the opposite of dog was not dog, while the boy himself insisted that the opposite of dog was cat. who was right?
my father and i got into the same argument. is a negation the same as an opposite? what is an opposite, anyway? the dictionary says that an opposite is: something contrary or radically different in some respect common to both.
so, opposites must be similar, yet radically different. the opposite of dog is not "tomato".
the conclusion my dad and i reached was that opposite is only an opinion. it is relative. a negation is not the same thing as an opposite.
its like what the petrified flower said about truth- it is in the eye of the beholder. the opposite of dog is indeed cat, but only because we think that it's true.
just something to think about: how about chocolate and vanilla?