Although writers on art long believed that African languages provided no specific technical vocabulary for aesthetics, Robert Thompson's research among the Yoruba suggests that this culture has a precise vocabulary for describing and evaluating the visual arts. According to the summary of his work in Frank Willet's introduction to African art, Thompson asked two hundred Yoruba to provide critiques of a set of sculpture and discovered nineteen criteria, "the most frequent being jijora, the moderate resemblance to the subject, a balance between the extremes of portraiture and abstraction. He was told repeatedly of a pair of twin figures that 'they look like somebody'. It is indeed one of the surprises of living in Yorubaland that one does frequently see people whose features remind one very forcibly of a particular sculptural style" [African Art, Thames and Hudson, 212]. Other important qualities include
Although Willet suggests some qualities of a possible pan-African aesthetic, he also cites the BaLega attitude toward sculptures used in their Bwami society rituals as a warning against both excessive generalizing and against assumptions that European and African aesthetic values always have much in common.