Terrace's article, "Thinking Without Language", I find that I agree with Terrace's conclusion that monkeys and apes are capable of coherent thought, without requiring language. On top of the compelling results of the tests with Terrace's four monkeys, there are several other instances of unconditioned responses which suggest thought shown by Koko the gorilla, in Patterson's studies, and Kanzi the bonobo, in Savage-Rumbaugh's studies.
In addition to Terrace's monkeys demonstrating the ability to remember and apply lists in order to solve problems without the involvement of language(Terrace, 2011), however, some other primates have been able to demonstrate their own problem-solving skills using language. Koko the gorilla has been able to combine a long list of words in order to form different word meanings without prompt, finding ways to refer to herself (Progress & Plans, web), and also ways of expressing 'ring', 'melon', 'swan', and 'gorilla' using the signs she already knew , using language freely(StateMaster - Encyclopedia, web).This shows an understanding about the meaning of the signs she used to build new ones, and that she registered a need for such words in the first place (rudimentary schemas?). This ability to combine words for different meanings would qualify Koko's signing as human language, by the grammars method of Noam Chomsky(Terrace,