Abstract: Examining the concept of “thing-in-itself” by Kant,we may see that Kant’s double implications of “thing-in-itself” are “unknowable” and “thinkable”,and we may distinguish the relationship between “thing-in-itself” and phenomena.Based on this,we may further demonstrate that “thing-in-itself” provides basis for the existence of freedom and make the co-existence possible fo
r freedom and the order of nature.It is because of the relationship and significance of this basis that makes the concept of “thing-in-itself” enter the field of practice along with the concept of freedom,and they together form the arc for the building of sense.

Key words: thing-in-itself, phenomenon, unknowable, thinkable, freedom