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In this article, St. Thomas determines what the ratio of goodness is. He distinguishes it into three, i.e., the "mode," "species," and "order." Central to this is the "species." For, the mode leads towards the acquisition of the species and order direct the species to the end.
Let's think of a good painter. The good painter, first, must be a painter. This is the possession of the "species" or "form." Yet, before this, the mode of the man's existence must be disposed towards receiving the form. Further, in order for the completeness of the act of being a good painter, he must be directed towards (i.e., ordered towards) good painting.