Of the two questions we get asked the most here at Aria Serious, I mean often enough that we feel we should mention them, are:
1.) Why does Bugs Bunny walk around the cartoon naked, but puts a bathing suit on when he goes swimming?
2.) What should I wear to the opera?
While we can't answer the first one, we can offer some guidance on the second one.
There are two camps here.
The first likes to think of a night at the opera as an excuse to get dressed up in their finest clothes. And a night at the opera does indeed make a good excuse to go shopping for that pair of shoes you'll only wear once (or in my case another tux as I seem to outgrow them each and every year). There are those that feel dressing up is part of the entire opera experience.
The second camp believes that a night at the opera is a night spent listening to some of the most beautiful music in the world so one might as well be comfortable. After all, it is about the music and drama onstage, not what the audience is wearing.
Opening night of the season, with the gala, tends to lean more to the first camp while Friday nights tends to lean towards the second. Of course you'll see tuxedos and gowns, suits and little black dresses, even jeans on all nights of the opera. And this is fine.
So to answer the question - wear what you want, but take a cue from Bugs please and at least put on a bathing suit before coming to the opera.