There are many semantic expansions in Japanese conditional expressions “To””Ba””Tara””Nara”. So far researches are mainly from logic semantic, functional pragmatic and comparative analysis and are rare from subjective cognitive motivation. This paper tried to explain the semantic expansions of Japanese conditionals from synchronic perspectives by using(inter)subjectivity theory. This paper concluded that Japanese conditionals appear as a continuum of ‘non subjectivity → subjectivity → intersubjectivity’. The semantic expansion of Japanese conditionals is closely related to the cognitive motivation, and being the result of objective construal and subjective construal upon the world.