In order to answer criticism of their methods and conclusions in teaching plastic-chip language to celebrity Sarah and other chimpanzees, and to clarify (perhaps with hindsight) the purposes of their research and their assessment of its results, the Premacks have carefully reviewed the experiments with an eye to what they demonstrate about Sarah's mental and language abilities and how her performance might have been misinterpreted. Sessions are examined or new sessions structured to test alternative explanations; different relationships between tasks and abilities are traced and considered; and double-blind tests are run to rule out inadvertent cues from trainers. From tests for such capacities as same/difference judgments, analogical reasoning, attribution of intention, equating left-right chip constructions with time sequence (for example, completing an apple/knife/cut-apple sequence), storing representations of objects in memory, and understanding proportion and conservation of quantity (Sarah had no trouble with this concept, which Piaget found inaccessible to children under six), the Premacks conclude that chimpanzees are naturally capable of many mental tasks beyond the grasp of bees or pigeons, for example; that language-trained chimpanzees attain impressive abstract capacities totally absent in the untrained (language training thus ""upgrades"" their minds); that humans all attain these capacities without special training; and that humans attain levels of abstraction far beyond the range of any chimp. Whether chimpanzees ""have language"" clearly depends on one's definition of language. The Premacks say yes because they emphasize the capacity for abstract representation as basic to language. However, in recent years they seem to have conceded an important point: they now call Sarah's strings of plastic words ""constructions,"" not sentences; they pinpoint the difference between constructions and sentences as the key difference between chimpanzees and humans; and they acknowledge that syntax is far beyond even bright, educated Sarah's representational capacities. After almost 20 years as leading researchers in the chimpanzee language arena, their moderation and conscientious distinctions should carry weight.