 Zhu Xi developed a theory of basic human propensities (nature, xing) to account for both the possibility of human evil and that of human goodness and perfectibility. On this theory, while (following Mencius, 372–289 BCE) insisting that people are basically good (well intended and sensitive to the sufferings of others), he accepted that the manner in which a person’s basic disposition is manifested is conditioned and at times contained by their specific qi endowment (native talents and gifts, qizhi), family and social environment, and other factors. Such factors together yield their empirical personality, intelligence, and aptitude for spiritual-ethical cultivation. Zhu accepted that there are real differences in individual disposition, character, as well as aptitude for ethical self-cultivation and realization, owing to individual variations in qi endowment, environment, etc. Furthermore, he argued that people can become bad or evil due, for example, to a coarse or sensual qi endowment, the bad influence of ruthless kin or friends, a selfish or harsh social environment, a cruel streak, etc. Nonetheless, following Mencius, he firmly believed that anyone who was sincerely committed to moral self-cultivation and was fervent in their moral practice would surely make progress in achieving moral realization if not sagehood.