defined a perfect thing as one that "possesses that of which, by its nature, it is capable." Also (Summa Theologica): "That is perfect, which lacks nothing of the perfection proper to it." Thus there were, in the world, things perfect and imperfect, more perfect and less perfect. God permitted imperfections in Creation when they were necessary for the good of the whole. And for man it was natural to go by degrees from imperfection to perfection. Duns Scotus understood perfection still more simply and mundanely: "Perfection is that which it is better to have than not to have." It was not an attribute of God but a property of creation: all things partook of it to a greater or lesser degree. A thing's perfection depended on what sort of perfection it was eligible for. In general, that was perfect which had attained the fullness of the qualities possible for it. Hence "whole" and "perfect" meant more or less the same ("totum et perfectum sunt quasi idem"). This was a teleological concept, for it implied an end (goal or purpose). God created things that served certain purposes, created even those purposes, but He himself did not serve any purpose. Since God was not finite, He could not be called perfect: for the concept of perfection served to describe finite things. Perfection was not a theological concept, but an ontological one, because it was a feature, in some degree, of every being. The 9th-century thinker Paschasius Radbertus wrote: "Everything is the more perfect, the more it resembles God." Still, this did not imply that God himself was perfect. The concept of perfection, as an attribute of God, entered theology only in modern times, through René Descartes — and in the plural, as the "perfections" of God. After Descartes, the concept of perfection as a principal concept in philosophy was upheld by other great 17th-century thinkers. In Benedict Spinoza's philosophy, however, there was no personal God, and perfection became a property of — even a synonym for — the existence of reality (that is, for the essence of things). Leibniz wrote: "As M. Descartes states, existence itself is perfection." Leibniz added: "Perfection, I call any simple quality, if it is positive and absolute, such that, if it expresses something, it does so without limits." At the same time, Leibniz also construed perfection, in his Monadology, in an utterly different way: "Only that is