  For Rosmini, the problem of being is finally considered under the three divisions of the science of theosophy: ontology, rational theology and cosmology, each of which must enter into the other if the science is to be complete. In fact, he maintains, it is impossible to speak of being in all its universal essence (ontology), without regard to the infinity and absoluteness of Being (rational theology), just as it is impossible to consider the world philosophically (cosmology) without taking its cause into consideration. Each of the three divisions of theosophy is as essential to the whole as, according to his example, the various vital organs are necessary to the existence of an animal. But the centre and substance of the whole treatise is teaching about God, without which there is no final explanation of the being or the world. Theosophy, therefore, is a single science which, through its division into three parts, is both one and three. Such an affirmation is paradigmatic of the thrust of Rosmini’s theosophy which eventually enables him to confront this rational science with the doctrine of the Trinity.