In a discussion around different kinds of musical theatre, I think the first step is to define the terrain of musical theatre. Musical theatre does not include all theatre that uses music. Musical theatre excludes – for example – opera, ballet, dance shows and plays with music.
The next step is to consider what we could broadly term narrative vs non-narrative musical theatre: this separates shows shows that deal with narrative (but not necessarily plot in the conventional sense) from compilation revues, vaudeville, burlesque and so on.
Once we’re in the terrain of narrative musical theatre, it is incredibly important to discern between categories that relate to form (operetta, musical comedy, musical play, concept musical, rock opera) and categories that relate to style (such as mega-musical, minimalist) or content (like jukebox musical or bio-musical) or narrative style (lyric, dramatic or epic).
The key to telling the difference is that the categories a form can be produced using any of the styles or bodies of content.
For instance, Jesus Christ Superstar – a rock opera – can be produced either as a megamusical or in a minimalist fashion, as could any operetta, musical comedy, musical play or concept musical. Consequently, a category defining the style of a production is secondary to one the defines its form.
In terms of content, a jukebox musical can take any the form of an operetta (look at all those shows that use music by classical composers to tell a story) or musical comedy (Mamma Mia!). The principle applies to musical plays, concept musicals and rock operas too. (To link with the example above, a musical about Jesus could, in theory, also be constructed in a jukebox fashion.) Similarly, a bio-musical might be constructed as a musical comedy (Funny Girl), a musical play (Gypsy) or a rock opera (the above-mentioned Jesus Christ Superstar). As such, categories related to content are also secondary to those related to form.
In terms of narrative style, Jesus Christ Superstar is epic: it is narrated to us by Judas. However, it could also be dramatic (no framework of narration or perspective) or lyrical (a one-person show where Jesus sings about his own life). But these shows could all be told in any of the forms listed above, also making the category of narrative style secondary to the category of form.
Any musical then can be defined by the intersection of these various categories.
I’d say that’s a solid foundation upon which a discussion of genre and form in musical theatre can be built and delivered a seminar to that effect several years ago when I was reading for my Masters degree in Theatre and Performance. The terrain is wide and complicated and fraught with ambivalence and contradictory perspectives, but I think I’ve outlined above quite clearly how I feel it all fits together.