The definition of art wasn't always the same, yet we are putting all the art ever made in history under the same microscope. That cannot accurately yield a definition of how our present culture defines art.
The fact of the matter is that our present culture determines what is art based on subjective reasoning, since there is no objective qualifications that must be met for something to be considered artistic. That's something that has been completely constant since the first music and art were created. There will never be a criteria that can explain what makes something artistic, and nobody will ever be able to explain one objectively since it's impossible for one to ever exist.