"The purity of their substance, the perfection of their circular motion, the unimpededness with which in thus moving they follow their own law, the incorruptibility of their being and the immutability of their courses—all these attributes make them in the sense of Greek philosophy "divine"... eminence of being. Among these constancy of being and immortality of life are paramount. Divine, therefore, are the stars, primarily not by their action but by the rank which they occupy in the hierarchy of things according to their immanent properties. And these are just the properties of order, eternity, and harmony which constitute the "cosmos" character of the All in general: this they represent most purely and completely. ...Beyond this ideal significance, their perfection is also the real guarantee of the duration of the whole, i.e., of the eternity of cosmic movement and life. Thus they are the most powerful assurance which the Greek affirmation of the world had been able to conceive."