Today’s question is: can you be a fan without being in fandom? And it’s corollary: can you be in fandom without being a fan? Perhaps counter-intuitively, the answer to both is “yes.”
Let’s start with some definitions first. A “fan” is, according to Merriam-Webster’s dictionary, is “an ardent admirer or enthusiast.” There are differing accounts of how the word came in to common usage, although the two most plausible origins stem from the words “fancy” (having a liking towards something) and/or “fanatic” (one who is excessively enthusiastic about a topic). As both possibilities result in similar connotations, and were in common usage around the same time, I won’t belabor the argument here.
“Fandom” then begins cropping up as a term in the early 1900s; the simple “-dom” suffix signifying the realm of all fans. Since fans are not necessarily located in a single geographic location, though, this realm is more metaphoric in nature. A collection of fans, wherever they might be.
It’s worth noting that, while formal fan clubs do exist, you obviously don’t need to become an official member to be a fan. Fandom is much less formalized as a rule, so “joining” is largely a matter of saying, “I’m part of this fandom.” Whether you go to conventions or participate in message boards or wear t-shirts proclaiming your interest, none of that is necessary to be a fan. There’s no real process to joining (or leaving!) a fandom. That said, if you never mention your fan interest to anyone, don’t participate in discussions about it, don’t make any reference to it outside of enjoying your interest by yourself, separated from others, then you’re not part of that fandom. Fandoms don’t require active participation, but if you deliberately isolate yourself from other fans, then you can’t be a part of that group. You’d be a fan without a fandom.
On the other hand, you could spend a great deal of time in and around a fandom, meeting up with others, sharing stories, marveling at whatever new content is out there… but still not care about the fandom’s subject of interest. Fandoms are about bringing people together and sharing with one another. And you can do that without concerning yourself with the subject at all. That person is likely a fan of the fandom itself; the types of people it attracts perhaps, or the types of discussions they have. Perhaps their friend or significant other was a fan first and introduced them to the fandom and simply by hanging around, they become part of the group despite not being primarily interested in their fannish pursuit.
I think both cases are fairly extreme and probably rather rare, but the question wasn’t how common they were, but whether they were possible at all. And in looking at how both fans and fandom are defined, you can see that their inherently loose structure, almost by definition, ensure the answer to both questions.