 As to the role of metaphysics among the sciences, this discipline for Avicenna holds a position of eminence with respect to all other branches of philosophy. The series of disciplines constituting the Šifāʾ amounts to a concrete classification of the sciences: in it, metaphysics functions as the “queen of the sciences” that ascertains the principles taken for granted by all the other sciences, and interconnects and orders hierarchically the system. Metaphysics is foundational insofar as it is the universal science of the existent qua existent (ontology). The scientific principles assessed by metaphysics are, on the one hand, the logical laws common to all the sciences (the axioms), and the universal concepts that every science uses without examining them (the primary concepts like “existent”, “thing”, “necessary”, “one”). On the other hand, metaphysics clarifies the principles that are proper to each of the particular sciences, i.e., their specific assumptions or hypotheses. Thus, metaphysics proves the very existence and the mode of existence of the subject-matters of the other sciences (for example, the existence of universals and categories in logic, of matter and form in natural philosophy, and of discrete and continuous quantity in mathematics).