My friend… If you want to argue about a point, which is based in a text, on a complex subject, maybe it’s better not to lead off with, “That’s arbitrary and without objective merit!” and then say, “Can you clarify the main point?” and then move to say “It’s a bad source, the author knew nothing.”
We are trying to measure a certain kind of goodness - which would entail a knowledge of what we mean by “good.” For Thomas, goodness is the appetitive apprehension of being (whereas truth is the cognitive or intellectual apprehension of being). So, the key is being, which is the ground for “doing”. Of COURSE xyz creatures do this or that stuff better than humans. That is not the point - which creature is nobler as a substance in general? It will be the creature with the form oriented towards a fuller appropriation of goodness, namely, a wider possibility for apprehending being. (The form of humanity is the rational part - as opposed to the matter, which is the bodily part.) The rational appetitive power (as opposed to the merely sensitive or vegetal appetites) can take in an indefinite amount of being by the process of abstraction of sensible forms (which is, nevertheless, a process mediated by the senses, which makes us lower than purely intellectual substances), thus is ordered towards something higher (viz. nobler) than mere animals and plants and dead things. This higher ordering - which is rooted in the being of the creature itself (rather than something which is tacked onto it - as rational animality simply is what a human IS) - makes humans nobler creatures than other bodily creatures.
That’s the basic argument. It is a systematization of common sense, which common sense is still unchanged since Aristotle was hanging out by the lagoons in Greece trying to figure out if a sea sponge is a plant or an animal. (By the way, still not too clear.)
