Understanding of lessons ---If everything is art...

I believe that if everything is art,there is no art in this world.
 What is ugly?What is beauty?Why?What we use to define the arts?These seemingly simple questions, are not simple.The equilibrium point of ugly and beauty for everyone is different.Even for different places or times.So it is difficult to find a everlasting principle of beauty or ugly for one thing.(I don't know if you can understand what I mean...please forgive my poor English...)
However, beauty is set off by ugly.Perhaps without beauty, ugly can also become beauty.Between beauty and ugly,there are no absolute standards.
In society, a thing can be identified as beautiful by most people,maybe it can be as beautiful for the time being. Perhaps when the times and people's aesthetic standards changed ,the thing is no longer beautiful.Perhaps the thing becomes a rubbish from art...