In Shushigaku, it is considered that 'ri (理)' (the law of everything, basis or standard for all things, 'it exists because it should be, and thus this is the law that should be so') exists in everything ('there is ri in each tree and each blade of grass'), and that people can reach 'sei (性)' (the 'ri' existing in each individual, the five constant relations and the five cardinal virtues of Confucianism) when they deeply understand 'ri' through study including reading about it.
朱子学では「理」（万物の法則であり、根拠、規範。「然る所以の故であり、且つ当に然るべき則」）はあらゆるものにあるとし（「一木一草みな理あり」）、そうした理について読書など学問することにより理解を深めた後に「性」（個々に内在する理、五常五倫）へと至ることができるとした。