Monkeys can understand the simple rules of grammar but the key element of all human languages is beyond them, a study at Harvard University has shown.
The research with cotton-top tamarins shows they are able to instinctively understand finite state grammar, involving the simple pairing of words.
However, they are not able to follow phrase structure grammar, the complex rules crucial to every human language.
Details of the US research are published in the journal Science.
"The technique that we used is one that's been long-used by people working with human infants," Harvard's Dr Marc Hauser told BBC World Service's Science In Action programme.
"The basic method is that you play [the monkeys] examples of things that... fit the rule that if you have an example from the category A, you will always have, immediately following it, an example from the category B."
Specifically, the tamarins were exposed to grammars based on meaningless syllables spoken by two different speakers - a male and a female.
One simple language featured alternating male and female voices, and it was this that the monkeys were seen to understand.
"You give them examples of that while they're sitting around the cage, basically eating the entire time, so they're passively listening to what's going on," Dr Hauser said.
"If they pulled out the rule that explains that variation, then when you give them new examples that fit that rule, they shouldn't be that interested. It's part of what they have heard before.
"If you give them new examples that violate that rule, then they should be interested and look towards the speaker."
In other words, the monkeys heard a phrase - the monkey equivalent of "the mouse" - and when they heard the word "the", they expected "mouse" to follow it. When it did not, they recognised this.
However, anything more complex was lost on them.
The scientists tried using more complicated patterns, such as multiple male and female voices, and found the monkeys registered no interest in any anomalies.
"The next step up is what in linguistics is referred to as a phrase structure," Dr Hauser said.
"We say 'the mouse and the cat, the dog and the chase, and ran away' - at some point you begin to lose track of who did what to whom.
"The point is that at an abstract level, in terms of the rule, you can keep growing that sentence.
"It's at that level of abstraction that you begin to generate the expressive power of language. The monkeys don't seem to be able to do that."
The work was intended to shed new light on the evolutionary differences between humans and lower primates.
Dr Hauser said that it could help pinpoint the key period in evolution where human communication began to develop to be different from that of other primates.
"After the divergence point between a chimpanzee-like animal and humans - about 5-6 million years ago - that kind of capacity had to evolve in the human lineage," he added.
"[This] allows us, for what we do today, to give the language that we have."