“Colorless green ideas sleep furiously.”

The sentence is syntactically and grammatically correct, yet utterly meaningless. Would you notice if someone said it to you in an otherwise normal discussion? Intuition says yes, but according to new research from Penn linguist Gareth Roberts and Yeshiva University’s Bruno Galantucci and Benjamin Langstein, the truth is most likely no.

These findings, published in Language & Communication, stem from a series of experiments conducted by Roberts and colleagues focused on how extensively people misunderstand each other in everyday conversation. 

“People are perhaps not quite as good at communicating as we think,” says Roberts, an assistant professor in the School of Arts and Sciences. “Not only that, but there might actually be quite a lot of miscommunication.”

During the first of three experiments, conducted in 2014, the researchers paired up 40 participants. Each set met in person, then went to separate cubicles to chat via instant messaging, with the goal of determining which colors differed in the cartoon they each viewed. Another pair, concealed from the first, conducted the same task, but for a different image. Partway through the experiment, the researchers secretly swapped the pairings; about a third of participants didn’t notice.

In a second study with much of the same set-up, participants discussed which pictured celebrity they would most want to befriend. Without disclosing their intention, Roberts and colleagues mixed two incoherent phrases into the computer-based discussion, referencing a celebrity not shown, for example, or stating the incorrect gender for another. Again, more than a third of participants couldn’t tell.

Because the conversations happened electronically, however, some have rationalized the initial findings, Roberts says. “Maybe it’s because the words are typed or participants aren’t paying attention to the writing, or they’re not getting the extra information you get from talking with someone face to face,” Roberts says. “You strip away a lot of real-world physical information when you’re instant messaging.”

Those questions led to the latest experiment, which tested miscommunication during in-person interactions. Here, the researchers paired individuals with a mole—called a “confederate”—who conducted a normal conversation then, eight minutes in, uttered the sentence, “Colorless green ideas sleep furiously.”

“They were told to do this when it was their turn to speak. They weren’t supposed to talk over the other person and were told to say the sentence very clearly,” Roberts says. “A minute later, we stopped the experiment.” Just 10 out of 30 participants sensed anything amiss, and of those, only one could identify the confederate’s weird sentence.  

“Not only does this show that the findings replicate in face-to-face conversation, but it happens more,” Roberts says. “People are worse at spotting weirdness [in person].”

Roberts offers several possible explanations: People might shoehorn what they think they heard into the current conversation’s narrative; they may not want to interrupt the dialogue to seek clarification; they may simply not pay attention; or perhaps reliably transferring information from one person’s brain to another’s matters less than the experience of the conversation itself.

“It’s relatively rare that we’re conveying information where the precise detail or wording matters. And when we have to do that, like when landing a plane, we have systems in place to make sure there’s no miscommunication,” Roberts says. “A lot of conversation is really about people using language to interact, but the actual information involved doesn’t matter.”