It feels to me like I see pouring over for poring over a lot these days in the sense of “study, ponder.” (“She pored over the manuscript looking for typos.”) However, the “it feels to me” approach to language is not very scientific, is it.
So the first stop is to look at some numbers. A COCA search for pour over yields 670 hits; for poured over it’s 363 hits; for pouring over it’s 254 hits. When I look through the context, many of these instances refer to pouring in the liquid sense (“melt butter and pour over the carrots”). There are certainly instances of pour(ing) over to mean poring (“He would buy maps and pour over them”). I suppose I could look through all thousand-plus cites and get a percentage, but I’m satisfied that there is a small but noticeable number of instances of pour/pore confusion.
Why would people mix up pour and pore? One relatively easy answer, I think, is that pour is a much more common word than pore. A simple search for each in COCA gives us these numbers:
pour: 15,383 hits
pouring: 8,618
poured: 12,642
Total: 36,643
pore (as a verb): 1,247 hits
poring: 872
pored: 562
Total: 2,681
If I’ve done my searches correctly, pour is about 13 times as common as pore. That’s a much larger difference than the relative frequencies of reign and rein, another pair that’s often mixed up. (I count reign as only 2.7 times more frequent than rein, using the same simple searches in COCA.)
So that’s one reason people might write pour over to mean “ponder”: they see pour (over) a lot more often than they see pore (over). And if people see pour over to mean “study,” as they do, it reinforces their notion that that’s the correct spelling.
I was also slightly surprised to learn that pour and pore are homophones for most people; Merriam-Webster and Dictionary.com list the same pronunciations for both words. Me, I make a distinction between pour (rhymes with “boor”) and pore (rhymes with “gore”). I have no idea where I picked up this distinction or how many other people have this difference. It would certainly help explain why people use pour for pore; namely, they don’t hear a difference (reign/rein again), which of course makes it that much harder to keep the words distinct.
Finally, there’s the semantic angle. If you’re not familiar with the verb pore, it can make sense to think about someone who’s “poured over” (hunched over) a book or map that they’re studying.
These factors—relatively (in)frequency, homonymity, and a semantic overlap (albeit with squinting)—are classic bases for an eggcorn. And sure enough, the pore/pour difference has an entry in the Eggcorn Database.
There are other pairs like this, including trooper/trouper and peek/pique, where one variant (trouper or pique) is rare enough that people might not even know there’s a difference. It’s easy to imagine that in an age before dictionaries, the lesser-known variant could disappear. (I’m sure that happened many times, but I can’t come up with an example right now.)
These days we can freeze the spellings of the less-frequent words. But it doesn’t guarantee that people who are writing casually are going to know about the variants. We just have to recognize that when someone writes pour over, they might mean pore over.