What is the specific theme being expressed in the play "Pygmalion"?

At the risk of sounding like Bill Clinton, what
specifically do you mean by the word "specific"? (If you're too young to get that joke,
check out the link below.)

Unless our name is George
Bernard Shaw, we can only attempt to say what is the theme of
"Pygmalion."  

In my humble opinion, there are two main
themes in "Pygmalion."

a) Distinctions of class (upper
class, lower class, etc.) are artificial.  If a "guttersnipe" like Liza Doolittle can be
trained to the point that she can be the star of a high-society ball, then what real
difference is there between the guttersnipe and the
princess?

b) Education can modify our behavior and our
attitudes, but only up to a point.  At the end of the play, Liza chooses to marry Freddy
and run a flower shop rather than live the high-life with Higgins.  She would be utterly
incapable of returning to the gutter--but she is just as incapable of dealing full-time
with Higgins's snobbery, intellectualism, and occassional forays into high
society.

Remember: theme is a matter of opinion.  Your
opinion must be reasonable and well-supported by the text, but it is still your
opinion.