This paper examines how Ralph Cudworth and Nehemiah Grew promote two different conceptions of 'life' for apologetic reasons : a generic one (life as something mental), and a specific one (life as vegetation). On the one hand, ‘mental’ features of life (i.e. sensation and intellection) are the best proof of its incorporeal nature, and this way, the best proof of the divine causation testified by vital phenomena. On the other hand, the ‘vegetative’ sense of life, regarded as the lowest common denominator of the group of things or properties that are called ‘vital’, is the best way to demonstrate both the presence of God everywhere throughout the whole universe and the unity of the creation. I show how the theological use of the notion of 'life', that requires these two different conceptions of vitality, prevents one from clearly distinguishing between animate and inanimate bodies.