And as a matter of fact perhaps the first great common and most obvious feature which strikes the mind reflecting on the visible universe is the feature of all-pervading change (κίνησις), movement, evolution, progress and regress, growth and decay; we see it everywhere in a variety of forms, mechanical or local change, quantitative change, qualitative change, vital change. Now the knowledge acquired by the study of things under this common aspect is called _Physics_. Here the mind abstracts merely from the individualizing differences of this change in individual things, and fixes its attention on the great, common, sensible aspect itself of visible change. But the mind can abstract even from the sensible changes that take place in the physical universe and fix its attention on a _static_ feature in the changing things. This static element (τὸ ἀκίνητον), which the intellect apprehends in _material_ things as naturally inseparable from them (ἀκίνητον ἀλλ᾽ οὐ χωριστόν), is their _quantity_, their extension in space. When the mind strips a material object of all its visible, sensible properties—on which its mechanical, physical and chemical changes depend—there still remains as an object of thought a something formed of parts outside parts in three dimensions of space. This _abstract_ quantity, _quantitas intelligibilis_—whether as continuous or discontinuous, as _magnitude_ or _multitude_—is the proper object of _Mathematics_. But the mind can penetrate farther still into the reality of the material data which it finds endowed with the attributes of change and quantity: it can eliminate from the object of its thought even this latter or mathematical attribute, and seize on something still more fundamental. The very essence, substance, nature, being itself, of the thing, the underlying subject and root principle of all the thing’s operations and attributes, is something deeper than any of these attributes, something at least mentally distinct from these latter (τὸ ἀκίνητον και χωριστόν): and this something is the proper object of man’s highest speculative knowledge, which Aristotle called ἡ πρώτη φιλοσοφία, _philosophia prima_, the _first_ or _fundamental_ or _deepest_ philosophy.(15)