[This is one of those speculative posts, so bear with me. I am not necessarily saying that I buy everything said here, but I do think it is is worth putting the model out there.]
It’s not too surprising that the Yeatses’ spirits address the source of artistic inspiration. Not only is it of personal relevance to W. B. Yeats, but the system they describe gives the aesthetic a key place. A Vision divides souls into two sorts, primary and antithetical. The primary souls are souls of action, the McBrides of the world in their various forms, but the antithetical souls are thoughtful souls, inclined to subjective, aesthetic, and intellectual pursuits.