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The curious case of and/or

Raj Singh/Carleton University

A parent tells a child, “You can have cake or ice cream.” The child announces the choice: “Both.” You might think this is just the kid being willful, demanding both treats instead of one. But with very young children, this type of impasse often arises for a different reason — they don’t understand the logical difference between the words “and” and “or.”

It’s also because of the way their brains work.

Imagine a teacher saying, “Some of my students passed the test.” You probably inferred right away that some students passed the test and some failed. This is because you unconsciously considered alternative sentences the speaker could have used — such as, “All of my students passed the test” — and interpreted what the speaker said in light of the options not chosen.

But many young children “don’t seem to conclude from ‘some’ of my students passed that ‘not all’ of them did,” says Danny Fox, a linguist at MIT and coauthor, along with lead author Raj Singh of Carleton University, of a paper forthcoming in Natural Language Semantics.


The same process that helps adults see that “some” means “not all” is called “alternative sensitive computation.” Because it’s so complicated, linguists long assumed that the reason children don’t always do it right is that their brains lack enough processing power or they don’t know enough to carry out the computation.

There is another possible explanation for why kids often misinterpret sentences whose meaning is plain to adults. Children may conduct exactly the same logical process as adults, but arrive at different conclusions because they run that process over a narrower set of alternative sentences.

The researchers presented kids aged 3 to 6 with pictures of characters holding different objects. In one set, some boys had an apple and the others a banana. A puppet described the picture with the statement “Every boy is holding an apple or a banana,” and the researchers asked the kids whether the statement was true.

Adults say true — each boy in the picture is indeed either holding an apple or holding a banana. But most of the kids said false. When asked why, they gave responses like “Because he’s not holding a banana” or “Because he’s just holding an apple.” This is exactly what you’d expect if they were interpreting “or” to mean “and.”


To understand the way adults interpret “or,” you need to take into account that “or” has “and” as an alternative.

Kids, while familiar with the word “and,” don’t intuit it as an alternative choice and so interpret “or” in a way that’s technically correct, but misses the speaker’s actual intent.

These results are consistent with the trend in linguistics to think of the real power in language as arising from short “function” words that stitch sentences together — words like “if,” “and,” “or,” and “why.” These words turn language from something that simply gives names to things (“table,” “rock,” “cup,”) into a logical system that, almost like computer code, makes sophisticated thinking possible.

Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.