Def.
vi.), that by reality and perfection I mean the same thing.

For we are wont to refer all the individual things in nature to one genus, which is called the highest genus, namely, to the category of Being, whereto absolutely all individuals in nature belong.
Thus, in so far as we refer the individuals in nature to this category, and comparing them one with another, find that some possess more of being or reality than others, we, to this extent, say that some are more perfect than others.

Again, in so far as we attribute to them anything implying negation--as term, end, infirmity, etc., we, to this extent, call them imperfect, because they do not affect our mind so much as the things which we call perfect, not because they have any intrinsic deficiency, or because Nature has blundered.

For nothing lies within the scope of a thing's nature, save that which follows from the necessity of the nature of its efficient cause, and whatsoever follows from the necessity of the nature of its efficient cause necessarily comes to pass.
As for the terms good and bad, they indicate no positive quality in things regarded in themselves, but are merely modes of thinking, or notions which we form from the comparison of things one with another.

Thus one and the same thing can be at the same time good, bad, and indifferent.