In my opinion, to answer the question "Are petticoats absolutely necessary to the Lolita fashion?" shortly and simply: No, they are not. You may now proceed to the comment section to let me know why I'm wrong if you feel the need to, or you can stay awhile and let me explain why!
Petticoats are important, but lucky for us this particular dress isn't the only one in the Lolita fashion.
Don't get me wrong, I think that a petticoat can make or break a borderline outfit Lolita, and lack of one can potentially ruin an otherwise completely fine Lolita outfit, but I think that there are a considerably large number of Lolita coordinates and dresses out there that don't necessarily need a petticoat to be considered Lolita. I feel that there's really no definitive thing you can say about petticoats being necessary throughout all of Lolita and it's definitely something that you need to take into consideration with each individual outfit.
Baby's iconic babydoll dress
Most iconic Lolita coordinate in Lolita history, or not Lolita at all?
Those that do own this type of dress and do wear it with a petticoat tend to wear it with a deflated tulle one, which does absolutely nothing for the poof, and functionally, looks exactly the same as wearing nothing under it. To those of you saying "But that counts because even a deflated petticoat is still a petticoat!" then what is the point at all of saying that a Lolita outfit needs a petticoat to be considered Lolita, even if that petticoat does absolutely nothing? At this point the petticoat becomes a completely arbitrary clothing item that cannot be seen and may or may not effect the look of the outfit in the slightest, you may as well say that Lolita can be defined by whether or not someone is wearing a ribbon tied around their waist under their dress. I feel that the importance of a petticoat stems not from the fact that it gives skirts a particular silhouette, especially considering Lolita skirts can come in a number of shapes and lengths and be deemed acceptable, but because it is part of a more general aesthetic that is far more important than mere shape.
If you want to see a few examples of Lolita without the poof, check out the blog No Petticoat Needed! It's more of an otome blog but there are a few Lolita outfits showcased.
Not a cupcake.
The truth is, Lolita isn't something that can be enirely defined by a few quick words, or a chart pointing to different style elements, or even a single blog post, no more than any other fashion can be. The importance of the petticoat is that it is part of the elegance and opulence of the Lolita aesthetic, even interpreted through the ultra kawaii or edgy and deconstructed sub-styles of the fashion.
That being said, just like any of the other aspects of the Lolita aesthetic, I feel like petticoats are part of a sort of sliding scale of Lolitaness. Similar to how a relatively plain loliable dress devoid of common Lolita details can be perfectly Lolita if it's coordinated properly, a dress with iconic Lolita elements, and coordinated with undeniably Lolita items, can still be Lolita even if it doesn't have the traditional silhouette.
This is all too often what you hear when someone says they think petticoats are optional, as well as any number of other Lolita fashion "rules". The truth is, Lolita is sometimes an overwhelming fashion and sometimes newbies (and even not-so-newbies!) might make some choices that might not exactly be the best, and having a set of guidelines is a good idea for the fashion to help anyone interested in wearing the fashion. However, we have to remember to stress that these are guidelines, and not rules. As someone who's been into the fashion for a very long time, and have had the chance to see how the community changes with the years, one particularly troublesome thing I've noticed is that when you lay down rules for newbies, those newbies grow into Lolitas assuming that these rules are set in stone.
Back in about 2006/2007 there was a very strong emphasis in the community on what is and isn't Lolita. The Western Lolita communities began questioning what it was that made something Lolita and were trying to, as a community, nail down the style. This was a pretty awesome thing for the community to be finally considering, however a lot of the "rules" that came from this era of new found self-reflection have stuck for many people as being the only way to define Lolita.
How often have you heard someone say that all Lolitas must wear blouses at all time, skirts may not be more than a certain number of inches above your knee, black and white dresses are instant Ita, or any number of rules touted as a set-in-stone truth? There's a pretty good chance that people believe these things to be absolute truths because, when they were first getting started, someone tried to steer them away from Itadom, but neglected to mention that, yeah, they're not really rules at all. Personally, I've heard such silly things more times than I care to. It's all well and fine to help a newbie out, especially in such a tricky fashion like Lolita, and especially with cringe-worthy scratchy lace skeletons hanging in so many of our own closets that we would like to spare other newbies from, but we have to remember to emphasize that these are not rules, but rather "learn to crawl before you can run" guidelines.
In emphasizing the importance of the silhouette above all else, I feel that many people have disregarded the general aesthetic of the fashion, leading to a lot of really watered down ideas of what makes something Lolita. I feel that this over-emphasis is just as misleading for budding generations of Lolita as the other rules have been.
So how do you help newbies?I recently asked EGL what people there considered the rules or defining features of Lolita to be, and one user, Carmidoll, brought up a very interesting idea: that Lolita can really only truly be learned through osmosis. This seems like a somewhat weird idea, but I realized that it's probably how we all truly learned how to define what Lolita is. By reading the Bibles, by searching for street snaps, by lurking Daily Lolita, by reading Lolita blogs, by talking about it with other Lolitas online, or by participating in our Local community. Lolita is really an immense fashion, and defined by so much more than just how high above your knees your poofy skirt lands that it's almost impossible to take in by reciting what amount to arbitrary fashion rules. It's really something we can only know after we've experienced it in some way.
If you have a friend who is interested in getting into Lolita and doesn't quite know where to start, by all means, let them know that it's a good idea to wear a petticoat, or that full-length dresses and barely-butt-covering skirts probably isn't the best choice for a Lolita outfit, remind them that some JSKs might look more put together with a blouse, but avoid trying to define the fashion by these things. Instead, share your Bibles with them, gush over newly released dresses with them, discuss trends and fads with them, even share clothes with them if you can. The best way to learn what Lolita's about is to participate in it in whatever way you can.
What are your thoughts on the subject? Do you think petticoats are mandatory or optional providing the outfit is right? Or to go above and beyond that, do you feel that not only are petticoats mandatory, but only specific shapes and lengths are? What exactly do you personlly find the defining features of Lolita to be?