The human function is "some sort of life of action of the part [part of the soul] that has reason. Aristotle divides reason into two parts: 1) the ability to obey reason, 2) the other as human beings having reason and thinking. This distinction marks the necessary emphasis on the required relationship of virtue as being both our ability to know virtue through reasoning and our ability to perform activity that actualizes that knowledge. The final piece of Aristotle's argument I'd like to recall is that, negatively put, natural capacities are not acquired by habituation; and positively understood, virtue is not a natural capacity and therefore is acquired by habituation.
I'm curious what others think Aristotle implies here of the ability for the mentally handicapped to cultivate virtue, and in this sense her ability to be happy? Also, do we see any parallels in Kantian moral theory as regards the implication that mentally handicapped citizens are equally incapable of cultivating the Good Will? And finally, we must consider not only the ability for one to have virtue (or the Good Will) but also what this implies of our responsibilities towards these people (as in Kantian moral theory we are, by the formal logic of its description of treating all rational beings as ends in themselves).