How to tell bad art and good art

Nowadays, there has been a widespread phenomenon that more and more artworks express in different styles.  It's very hard for us to distinguish bad art and good art. This issue also has been widely debated in the world.  Some people think that good and bad are personal distinctions, it's depending on the quality of the viewer's taste.  However,  others believe that there is a "line" to divide bad art and good art and no one is clear where is the "line". In my opinion, when we to judge an artwork, the viewer's taste is very important, we need have the ability to tell which one is crap art.  The decision is based on our knowledge. If we want to have this ability, we need to read art-related books and go museums and galleries to appreciate more masterpieces.