Andrew Heisel is a writer in New Haven, Conn.

(LM Otero/AP)

I am a writer, which is why it’s particularly embarrassing that I sometimes type the word “right” when I mean to type “write.” Shouldn’t I know better? Just yesterday, I typed “there” when I meant “their.” And I’ll even admit that I’ve committed the most mocked grammar error on the Internet: “your” instead of “you’re” (and vice versa). And yet, I have stood by and watched on Twitter and in comment sections as people are pilloried for making these egregious blunders, knowing I’ve been just as guilty. I’ve even snickered when someone commits a grammar crime while writing a particularly objectionable opinion about politics or sports.

Calling out other people’s grammar mistakes has become such an Internet pastime that Weird Al Yankovic made a music video about it and a Twitter account called the Grammar Police has attracted more than 19,000 followers. The Grammar Police bot publicly shames people for making little language errors, such as using “hear” for “here,” and lets the world know exactly what grammar rule the offender broke.

But people don’t need to be corrected any more than they need to be ridiculed. I know the rules for how these words should be used and spelled, and I’m sure most who make these mistakes know them, too. What I really wanted to know is why we make these slip-ups anyway.

To find out, I spoke with Maryellen MacDonald, a cognitive psychologist at the University of Wisconsin-Madison, who studies how the brain processes language. She said that even though your brain knows the grammar rules, other forces override that knowledge. The brain doesn’t just store words like a dictionary does for easy retrieval, it’s more of a network. You start with a concept you want to express and then unconsciously consider several options from its associative grouping and quickly select one. For instance, if you’re explaining how you hit a ball, you might cycle through the concept of a stick, a pole and a bat. Next, your brain will use sound to aid its expression. Here’s where things can get tricky.

“Usually we pay a lot of attention to pronunciation while we’re typing because it’s usually a really good cue how to spell things,” MacDonald said. But homophones can trip this process up. “When someone types ‘Are dog is really cute’, it’s not that they don’t know the difference between ‘are’ and ‘our’; it’s that the pronunciation of ‘our’ in the mind activated the spelling ‘our’ but also ‘are.’” Even nearby “hour” might come out, she said.

The brain doesn’t always consult a word’s sound, but studies have shown that it frequently falls back on it, and sound tells us nothing about the difference between “you’re” and “your.” Research on typing errors reveals that sound creates even odder mistakes, such as people writing “28” when they mean to type “20A.” It’s no wonder that people who know better will routinely confound closer pairings such as “it’s” and “its” or “know” and “no.”

Tom Stafford, a cognitive psychologist at the University of Sheffield who is currently involved in a massive study of Wikipedia edits to see what they reveal about how the brain processes language, told me that we usually get these spellings right less because we apply a rule than because of our brains’ wiring. “When you first start typing, you don’t have any habits,” he said, “and then as you become fluid, that skill is based on the assemblage of routines that you don’t have to think about.” Over time, motor systems allow you to act without belabored thought. But there’s a cost to being able to type 60 words per minute: Sometimes those habits steer us wrong.

For instance, if a friend texts that she’s “going to a concert” and you want to tell her you’re also going, you might type, “I’m going, to,” instead of “I’m going, too.” Your brain is used to hearing the word “going” followed by the word “to” (as in going to work/school/etc.) and it just saw the phrase used that way in your friend’s text. Conversely, in sentences that should end with the preposition “to,” people often write “too,” because that word more frequently concludes a sentence. Habit, usually so helpful, sometimes leads us astray.

We’ve long known that habits have the power to overwhelm intentions. In the 1880s, psychologist William James described the man who goes to his room to change clothes and suddenly finds himself undressed and in bed. “He began the routine correctly,” Stafford said, but then lost focus and did the more high-frequency action. In extremely grave cases, this slip from conscious intention into repetition of habit has led people to forget their children in their cars. In extremely trivial ones, they type “then” when they mean “than.”

Regardless of what you intend to do, “there’s this tendency for these high-frequency things to assert themselves,” Stafford said, “and that’s particularly true when you’re not paying attention or you’re in a rush. And when we’re typing, we’re always in a rush.”

Slips of the brain also create less common mistakes. Consider all these people trying to make a joke about calling 911 and inadvertently typing “call 9/11.” You don’t say the two the same way, but somehow the constant invocation of 9/11 helps it supplant the phone number. Or consider my fairly uncommon last name, Heisel, which for my entire life has appeared on name tags and forms as “Heisler.” That surname is not all that common, either, but it’s familiar enough that the brain’s autopilot often chooses it over mine. Similarly, professor Maryellen MacDonald told me, “I’ve been Mary Anne all my life.”

If we can mistakenly deploy words we rarely see, it’s no wonder that the basic building blocks of the language, such as “to” and “too,” would continually intrude upon each other’s space. We can take care to make sure the right one comes out, but, MacDonald said, “cognitive control is hard work. … It’s putting the brakes on something you would typically do.” As studies of attention show, you only have so much to go around before your mind falters.

Of course, people can and should proofread (a practice the brain complicates as well), but we can never fully curtail these slips that rapid-fire media like Twitter bring to the fore. Mocking another person for making one of them is like mocking a heart for skipping a beat. Errors are a routine part of our cognitive systems, as likely to happen to you as to me, as to that guy with the terrible opinions ranting beneath an article. And people certainly don’t need reminders of the simple rules by a program such as  Grammar Police, either. The bot is really just a reminder of the difference between the tidy logic of a machine and the wonderfully messy mental architecture of humans.

But if to err is human, so, too, it seems, is wishing you weren’t. Maybe the pleasure in following that bot is that it allows you to pretend, 25 times a day, that you’re perfect and other people’s foibles are not your own. Even people who understand precisely how helpless we are to avoid these little missteps can fall prey to this desire. MacDonald said she still ends up chastising herself when she realizes she’s made them.

And though she and Stafford helped me feel less shameful about committing these errors, my focus on them did nothing to stop me from making them repeatedly while typing this article. Sometimes, knowledge is powerless.

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