This traditional view has been challenged by Chinese, Japanese, and Western scholars. The Qing dynasty philologist Cui Shu argued on linguistic ground that the last five books were produced much later than the rest of the work. Itō Jinsai claimed that, because of differences he saw in patterns of language and content in the "Analects", a distinction in authorship should be made between the "upper "Analects"" (Books 1–10) and "lower "Analects"" (Books 11–20). Arthur Waley speculated that Books 3–9 represent the earliest parts of the book. E. Bruce Brooks and A. Taeko Brooks reviewed previous theories of the chapters' creation and produced a "four stratum theory" of the text's creation. Many modern scholars now believe that the work was compiled over a period of around two hundred years, some time during the Warring States period (476–221 BC), with some questioning the authenticity of some of the sayings. Because no texts dated earlier than about 50 BC have been discovered, and because the "Analects" was not referred to by name in any existing source before the early Han dynasty, some scholars have proposed dates as late as 140 BC for the text's compilation.