Be wary of anyone citing "authority" in the field of art. Art is about creating. So there will always be those who are creating new things, some of which will not be appreciated. Remember that the impressionists, the cubists, the surrealists, the abstract expressionists, were all shunned in their time. And today, there are those who would tell you that there is only one acceptable kind of art.
From my vantage point as an art teacher, often dealing with beginners who would put me on a pedestal because of my greater experience, I find it particularly important to remind myself of this. I am usually teaching "the basics." And the basics are important. But it is also important to validate the creation of the individual artist. He or she may not have the scene exactly right, or the colors, but that creation nevertheless is important.
The field of art is full of authorities. Listen to them, because they have knowledge. But beware of wholesale acceptance.
Here's an example: A student recently asked if she could use a fan brush to make the leaves on the trees. I immediately replied that the purpose of the fan brush was blending. Then I backtracked, because you could use a fan brush for foliage, and many do. It's not its original purpose, but — hey — why not?
Painting About.com website has more on the use of the fan brush.