Phish began its semi-regular New Year’s run at Madison Square Garden on Wednesday, the first of its four straight nights of shows there. The concerts are sold out. If you don’t have a ticket and don’t follow Phish, it means that you’ll see excitable, woodsy-looking men with beards in Midtown bars before 7:30 and after 11:30 p.m. The concerts will in no other way affect you. They do not intersect with contemporary aesthetics or dynamic social currents.

If you have a ticket or another way in, you enter a self-contained polity. Phish has been running since the mid-‘80s, with a five-year hiatus in the aughts. Its concerts have become markers in fans’ lives, no matter whether they’re mundane or special. And all the details of the concerts — especially those at Madison Square Garden, where this Vermont band has played more than anywhere else other than a couple of clubs in Burlington during the early years — take on their own narratives, myths and rituals, as within a fictional universe.

Which is to say that no action onstage or in the audience stands alone; everything is understood in relation to the biography of its repetition and variation. (Here we are talking about ceremonial glow-stick-throwing from the upper tiers; the regular inclusion of something new or rarely played in the set list; the audience yelling the final line in the song “Bathtub Gin” and the development of that song that comes after that yell.) Knowing what to do and how to react at a Phish concert is a kind of soothing fantasy version of life, in which everything is documented and yet memory is rewarded, the unexpected arrives at knowable junctures, and the old gang never goes away.