You can find and print out a digital simulacrum, but to fully understand the historical meaning of a genuine Purity Test you need to have held a dog-eared, much-stapled, much-passed-around version—or else one copied illicitly, toner still warm, in the back room at a friend of a friend’s weekend job. Once kept energetically (if sheepishly) from grown-up eyes and now ­familiar enough in some quarters to be worthy of parody, the Purity Test is a monument to many things, but most of all to the durability of pre-internet, semi-samizdat nerd culture. Anyone between the ages of, oh, thirty and fifty who ever played Dungeons & Dragons seriously, or who knows what a BBS was, has probably been in the same dorm room, basement, or bedroom with a copy of the test. (Wikipedia, for what it’s worth, finds a “purity test” from the 1930s, but traces this version’s origins to the early 1980s, at MIT.)

“Purity” is the opposite of sex: the test is, mostly, an exploration of sex, its preliminaries, its substitutes, its components, and its sometimes-grody, sometimes-­baroque variations, written by and for and about ­readers for whom it’s almost all new and mostly untried. The test comprises four hundred yes-or-no questions (“Have you ever…”), usually about things one might do in the course of a hookup, or during an all-out orgy, or on an unusual date—though some of them cover things you might do by yourself (for example) with someone else’s clothes. Early questions could generate plots for young-adult ­fiction: “Have you ever… used tickling as a pick-up, get-to-know-you-better routine? …secretly lusted after someone without that person knowing? ­…stuffed your bra if you are female, or stuffed your pants if you are male?
…gone steady with multiple people at the same time without all of the people aware of what you were doing? …gone steady …with all of them aware?”

Some questions are jokey and sweet (“…made an X-rated snowman?”), some overtly informational: a three-word query about anal beads takes three additional ­sentences to explain what they are. Of course, virgins taking the test will reveal themselves as such (question 153), but they are just one point in a continuum: you may have had sexual intercourse, but “have you ever had sexual intercourse more than 10 times with one person? …more than 5 times in a 24 hour period? …more than 10 times in a 24 hour period?”

The test also launches...