closest analog to their understanding of universal grammar in the late 20th century are Greenberg's linguistic universals. The idea of a universal grammar can be traced back to Roger Bacon's observations in his Overview of Grammar and Greek Grammar that all languages are built upon a common grammar, even though it may undergo incidental variations; and the 13th century speculative grammarians who, following Bacon, postulated universal rules underlying all grammars. The concept of a universal grammar or language was at the core of the 17th century projects for philosophical languages. An influential work in that time was Grammaire générale by Claude Lancelot and Antoine Arnauld. They tried to describe a general grammar for languages, coming to the conclusion that grammar has to be universal. There is a Scottish school of universal grammarians from the 18th century, as distinguished from the philosophical language project, which included authors such as James Beattie, Hugh Blair, James Burnett, James Harris, and Adam Smith. The article on grammar in the first edition of the Encyclopædia Britannica (1771) contains an extensive section titled "Of Universal Grammar". This tradition was continued in the late 19th century by Wilhelm Wundt and in the early 20th century by linguist Otto Jespersen. Jespersen disagreed with early grammarians on their formulation of "universal grammar", arguing that they tried to derive too much from Latin, and that a UG based on Latin was bound to fail considering the breadth of worldwide linguistic variation. He does not fully dispense with the idea of a "universal grammar", but reduces it to universal syntactic categories or super-categories, such as number, tenses, etc. Jespersen does not discuss whether these properties come from facts about general human cognition or from a language specific endowment (which would be closer to the Chomskyan formulation). As this work predates molecular genetics, he does not discuss the notion of a genetically conditioned universal grammar. During the rise of behaviorism, the idea of a universal grammar (in either sense) was discarded. In the early 20th century, language was usually understood from a behaviourist perspective, suggesting that language acquisition, like any other kind of learning, could be explained by a succession of trials, errors, and rewards for success. In other words, children learned their mother tongue by simple imitation, through listening and repeating what adults said. For example, when a child says "milk" and the mother will smile and give her child milk