 The second doctrine is the modulation and gradation of existence (tashkik al-wujud). The semantics of the term ‘existence’ and its modulated singularity commits Mulla Sadra to a reality that is equally modulated and singular. Existence is a singular reality, as the phenomenal experience of existence as multiple is illusory. But multiplicity in this world still needs to be explained. Different existents in this world are thus different, intense degrees of a single whole. Thus there is a horizontal and a vertical hierarchy of existence that is connected and involved in a whole chain of existence. The particular degrees of existence are not stable substances in the Aristotelian sense, and thus neither is Sadrian ontology concerned with a multiplicity of substances or the problem that would be raised by the objection: how can all things be one substance? Gradation addresses one of the key problematics of metaphysics that arise from Aristotelianism: “being is predicated in many ways” (Aristotle, Met. 1028a10). Being is a common term that is applied to a number of contexts and expressions: the mental context (mental being, conceptual being), the spoken context (being in speech), the written context (inscribed being), and the real context (concrete, extra-mental being). In all these contexts, being is a shared notion and reality expressed in different ways. But perhaps the most intriguing aspect of the doctrine is the claim that, not only is being the source of commonality, the focal meaning of the instances of being as the Aristotelian tradition would have it, it is also the source of metaphysical variance or distinction, because the hierarchy of being is differentiated through degrees of intensification and debilitation of being (ishtidad wa tada‘‘uf). Thus the old metaphysical debate about the One and the many is settled in favour of both: being or existence is both singular and multiple. The doctrine of the gradation thus provides an explanation for the nature of spiritual hierarchies and the different abilities and dispositions of people but also insists upon the ultimate singularity of human existence. Thus the ethical implications of the doctrine are a thorough social and ontological equality of existents (including humanity, animals, and so forth) coupled with an intellectual and spiritual hierarchy, order, and inequality. Mulla Sadra summaries modulation in the following manner: