Generations of scholars have debated the historicity of Laozi and the dating of the "Tao Te Ching". Linguistic studies of the text's vocabulary and rhyme scheme point to a date of composition after the "Shijing" yet before the "Zhuangzi". Legends claim variously that Laozi was "born old"; that he lived for 996 years, with twelve previous incarnations starting around the time of the Three Sovereigns before the thirteenth as Laozi. Some Western scholars have expressed doubts over Laozi's historical existence, claiming that the "Tao Te Ching" is actually a collection of the work of various authors.