Leaving a Mark
Of significant importance to some of the Charles family's men is the idea of leaving a mark on the world. Boy Willie expresses this most explicitly in his speech about his need to do something that will last in the world, to make a mark on a tree that says "Boy Willie was here." This hearkens back to the piano itself. Boy Willie's great grandfather also felt the powerful urge to leave a mark, and he did it by carving "we were here" into the wood of the piano. The irony is that Boy Willie wishes to sell the elder Boy Willie's statement in order to make his own.
Femininity
Berniece's femininity is a disputed ground in the play. Is she still a woman if she doesn't have a man? Berniece argues yes, certainly, and any modern audience wants to agree. But Wilson complicates this question by analogizing Berniece's refusal to take a man to her refusal to play the piano. We are made to wonder if being alone is really how Berniece belongs, or if she is hiding from herself, just as she hides from the piano. This connects to the clearly gender-coded way in which history and sorrow are presented, as inextricably tied to the matrilineal heritage of the Charles family. The implication is that Berniece's femininity, vis a vis her romantic life, is impeded by the legacy she was left as the only adult female in the family.
Music
Music is of course a very vibrant presence in a play named after an instrument. The instrument of the title, which holds a prominent place on stage for the length of the play, is a white instrument, part of the western musical tradition. But the only white music ever played on this piano is a few bars plucked out by the beginner Maretha - and she is quickly stopped by Boy Willie and his boogie woogie. The piano is appropriated for the music of the Charles family and their community, and as such music is made just as much of a cultural battleground as the piano itself.
Property
The concept of property is woven densely through The Piano Lesson. What is property? What can be owned? The Charles family was once property. Boy Willie seeks to own property of his own, believing property to be the key to success. The piano defies property-ness, becoming embued with spirits and a life of its own. Can it be property if no one - not the Charles family as a whole, not Berniece and Boy Willie, not Sutter - can make a complete claim to its ownership?
Ownership
Deeply entwined with the previous theme, the concept of ownership also brings into play questions of non-material ownership, vis a vis history and sorrow. Who can claim the Charles family history? Who wants to? Berniece feels that she inherited the right to the piano and part and parcel of inheriting her mother's piano. But her brother connects the ownership of the history to the patrilineal inheritance of the desire for a better life, claiming that their father would have approved of the plan to sell the piano for a plot of land. The division falls on gender lines - do men or women have a stronger claim to the community's history?
Overcoming death
As The Piano Lesson is fundamentally a ghost story, it features a lot of death overcome - in the form of Sutter's spirit haunting the piano, yes, but also the Ghosts of Yellow Dog continuing to protect their family from beyond the grave. But the theme is extended past the literal representation in the ghosts, to Boy Willie's claim that he has overcome death by transcending the fear of dying. He achieved this by killing a cat and discovering that he, like the white man, could wield death as a weapon. And in the end, Boy Willie truly does overcome death by wrestling its ghostly personification, and driving the spectre from the house.
Object vs Artifact
This is the fundamental problem that animates the entire play. Berniece wants to preserve the piano, untouched, unplayed, as an artifact of the family's history and suffering. The piano has a symbolic meaning separate from its practical or monetary value, and in Berniece's eyes it should be protected and preserved. But Boy Willie sees the piano only as an object, not as an artifact, and therefore he looks at it and his eyes fill with dollar signs. The understanding of the piano as artifact comes from the gut, and Boy Willie doesn't have it - to him, Berniece might as well be framing a $100 bill on the wall. The dual roles and interpretations of the piano form the backbone of the entire conflict of the play.
