Study
Can an ape create a sentence?
Terrace, H. S.; Petitto, L. A.; Sanders, R. J.; Bever, T. G.
Science, 1979
A chimpanzee was raised and taught sign vocabulary in a project designed to demonstrate ape syntax. Rather than relying on teachers' contemporaneous notes, the team analysed videotape frame by frame, examining what immediately preceded each of the animal's signs.
- Studied in
- Pan troglodytes
- Sample size
- 1 one chimpanzee, with frame-by-frame analysis of recorded sessions
The great majority of the chimpanzee's signs were prompted: they reproduced signs a teacher had made moments earlier, or were produced while the teacher was signing. Apparent multi-sign combinations were largely repetition and did not show consistent word order or increase in length with development, unlike the utterances of a signing child. Re-examination of published records from other ape-language projects showed comparable prompting.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
The evidence for syntax in signing apes does not survive frame-by-frame analysis; the animals learned to produce signs that produced rewards, without grammatical structure.
How NatureHQ reads it
This is not a paper claiming apes are stupid, and it is regularly misrepresented as one. What it established is a methodological point that had been missed for a decade: a human teacher who wants an animal to sign will cue it without noticing, and contemporaneous notes cannot detect that — only the tape can. The finding applies to the claim about grammar. It does not touch what apes demonstrably do: learn hundreds of symbols, use them intentionally, and communicate about things they want. The honest summary is that apes acquire vocabulary and do not acquire syntax, and that the difference between those two is most of what the word "language" is doing.
- One animal in one project; conclusions about other projects rest on re-analysis of their published material.
- A negative result about a particular training regime, not a demonstration of an upper bound on ape capability.
- Later work with bonobos raised in a language-rich environment from infancy reported comprehension the design here did not test.
Watching the tape instead of reading the notes
When a signing ape produces a string of signs, is it composing or copying?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: American Association for the Advancement of SciencePublished in Science or Science Advances (AAAS).
doi.org/10.1126/science.504995
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-11.