This paper aims to deal with a common problem underlying contemporary theories of the nature of living systems: the consideration of time as an extrinsic variable. Broadly speaking, most of these theories define the living being as a system engaged in a relationship with the environment, and focus on activities of self-organization and/or self-maintenance. In other words, they all presuppose a concept of the living being as a stable structure that needs to maintain its stability. However, it is necessary to realize that the living being is not a “structured reality” but a reality on its way to becoming structured. For this reason, time belongs intrinsically to the living being. From this perspective, the aforementioned theories all fall captive to their aprioristic understanding of life, and are limited by their own model. To correct this oversight, the paper introduces the constitutional paradigm as a new approach to the study of living processes, which takes as its starting point the living being as “structuring reality”.