I was always under the assumption that switching tenses was to be avoided in writing. Lately, however, after paying closer attention, I noticed that fiction in present tense will sometimes switch. So what is the rule? What am I missing?
In Chuck Palahniuk's "Guts," nearly every few paragraphs he'll jump from present to past then back to present.
Another friend of mine, a kid from school, his older brother in the Navy said how guys in the Middle East jack off different than we do here. This brother was stationed in some camel country where the public market sells what could be fancy letter openers. Each fancy tool is just a thin rod of polished brass or silver, maybe as long as your hand, with a big tip at one end, either a big metal ball or the kind of fancy carved handle you'd see on a sword. This Navy brother says how Arab guys get their dick hard and then insert this metal rod inside the whole length of their boner. They jack off with the rod inside, and it makes getting off so much better. More intense.
...
He's got to share a room with old people getting their guts worked on. He says how they all have to share the same television. All he's got for privacy is a curtain. His folks don't come and visit. On the phone, he says how right now his folks could just kill his big brother in the Navy.
On the phone, the kid says how--the day before--he was just a little stoned. At home in his bedroom, he was flopped on the bed. He was lighting a candle and flipping through some old porno magazines, getting ready to beat off. This is after he's heard from his Navy brother. That helpful hint about how Arabs beat off. The kid looks around for something that might do the job. A ball-point pen's too big. A pencil's too big and rough. But dripped down the side of the candle, there's a thin, smooth ridge of wax that just might work. With just the tip of one finger, this kid snaps the long ridge of wax off the candle. He rolls it smooth between the palms of his hands. Long and smooth and thin.
Or take Junot Díaz's The Brief Wonderous Life of Oscar Wao
She was standing in front of the medicine cabinet mirror, naked from the waist up, her bra slung about her waist like a torn sail, the scar on her back as vast and inconsolable as a sea. You want to return to your book, to pretend you didn't hear her, but it is too late. Her eyes meet yours, the same big smoky eyes you will have in the future. Ven acá, she commanded. She is frowning at something on one of her breasts. Your mother's breasts are immensities. One of the wonders of the world. The only ones you've seen that are bigger are in nudie magazines or on really fat ladies.
In Guts, there are stories within a story, and as long as they are consistent within the sub-stories, it's fine.
In the excerpt from Diaz, the first sentence sets the scene (in past tense).
Weird how in Chuck's I'm totally okay with it and in Diaz's I hate it outright. I think it's the use of voice... and lack thereof.
I was always under the assumption that switching tenses was to be avoided in writing.
That is generally accepted as true for transparent and static narrators. If your narrator is like a camera, or a fly on the wall, then shifting tenses can be very disorienting. Shifting perspectives (tense/pov) implies agency, or an active character directing the shift... with transparent narrators we allow more for pov shifts, probably because cameras move around. With agent narrators we allow more for tense shifts, probably because people exist and relate to each other (and themselves) across time. Really active narrators can get away with both, really static narrators can't really do either.
Lately, however, after paying closer attention, I noticed that fiction in present tense will sometimes switch. So what is the rule? What am I missing?
Well, just as it is perfectly okay for you to switch tenses two times in three sentences in your post, it is okay to do so in fiction. Because you as a speaker have agency and can direct your speech through the perspectives that will generate the most interest or information for the reader. The same goes for an active narrator who is telling a story. Especially if they are also characters in the story they are telling.
If there is a rule, it'd be something like "Use the perspective that generates the most interest and/or information." If that means not shifting, then don't. If it means shifting, then do.
That is generally accepted as true for transparent and static narrators. If your narrator is like a camera, or a fly on the wall, then shifting tenses can be very disorienting.
^Nailed it