Now we showed in the Appendix to Part I., that Nature does not work with an end in view. For the eternal and infinite Being, which we call God or Nature, acts by the same necessity as that whereby it exists. For we have shown, that by the same necessity of its nature, whereby it exists, it likewise works (I. xvi.). The reason or cause why God or Nature exists, and the reason why he acts, are one and the same. Therefore, as he does not exist for the sake of an end, so neither does he act for the sake of an end; of his existence and of his action there is neither origin nor end. Wherefore, a cause which is called final is nothing else but human desire, in so far as it is considered as the origin or cause of anything. For example, when we say that to be inhabited is the final cause of this or that house, we mean nothing more than that a man, conceiving the conveniences of household life, had a desire to build a house. Wherefore, the being inhabited, in so far as it is regarded as a final cause, is nothing else but this particular desire, which is really the efficient cause; it is regarded as the primary cause, because men are generally ignorant of the causes of their desires. They are, as I have often said already, conscious of their own actions and appetites, but ignorant of the causes whereby they are determined to any particular desire. Therefore, the common saying that Nature sometimes falls short, or blunders, and produces things which are imperfect, I set down among the glosses treated of in the Appendix to Part I. Perfection and imperfection, then, are in reality merely modes of thinking, or notions which we form from a comparison among one another of individuals of the same species; hence I said above (II. 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.