If we compare the later account of ratio and proportion in the Ethics with the earlier one of the Short Treatise on God, Man, and his Wellbeing we find two things. First, the Ethics includes within thinking features of proportion that had been attributed to the body alone in the early work. Second, the Ethics account characterises the infinity of Nature (and not just the particulars within it) in terms of ‘proportion’, namely, as an ordered and nested infinite system composed of subsystems. Spinoza has introduced the homeodynamic force of proportion that maintains the individuality – identity and persistence – of bodies in the Short Treatise into his accounts of the operations of the mind in the Ethics. And he has rethought embodied infinite Nature in the terms that he had formerly reserved for the coherence of singular bodies.

The maintenance in each of us and in all things great and small of a dynamic and unique individual equilibrium of motion and rest is captured by Spinoza in the notion of maintaining a ratio, a thing's proportion. In the early Short Treatise Spinoza had attributed this dynamic self-preservation to the body alone, mind merely passively figuring the dynamic of the body. In the later Ethics, however, mind has come to be understood in the proto-biological terms formerly reserved for body alone. For here, the self-maintenance and self-ordering energy of the individual body, its ratio, has come to include and be identified as well with a life-sustaining desire for mental self-perpetuation and self-furtherance – the conatus of the mind. In the Ethics Spinoza offers an account of thinking as a dynamic, ongoing, and integrative mental activity which has various degrees of well-functioning, so that he comes to biologise the mind more fully as he accounts for its functioning in the homeodynamic terms of ratio that he proposed for the singular body alone in the early dualistic theory of the Short Treatise. Ratio in the Ethics has come to be invoked to account for both the individuality and coherence of particular bodies and also for their expansion within nested larger extensional organisations or systems to infinity.