The external activity of Soul is nature, which is just the intelligible structure of all that is other than soul in the sensible world, including both the bodies of things with soul and things without soul (see III 8. 2).
"Human good," he writes, "turns out to be activity of soul exhibiting excellence".
It is also found in the activity of soul, which as a principle of 'external' desire images the paradigmatic desire of Intellect.
On the other hand, he also takes it that there is a restricted class of activities that the soul is responsible for in some special way, such that it is not actually the case that the soul is responsible in this special way for all of the relevant activities that living organisms engage in.
It must also keep to the way of justice regarding both character traits and actions, for these activities help the soul in conceiving of what is true and persevering in its inquiries.
For human beings the ultimate good or happiness (eudaimonia) consists in perfection, the full attainment of their natural function, which Aristotle analyzes as the activity of the soul according to reason (or not without reason), i.e., activity in accordance with the most perfect virtue or excellence (EN I.7.1098a7 17).
As a reviewer for the Times observed in 1982: > With Trevor as with Joyce one often has the sense of gazing down through the lucid surface of a personality to the dark, ambiguous activity of the soul.
This account ties happiness to excellent activity of the soul.
The missing link is that achieving the mean is also excellent activity of the soul.
Of course, Aristotle argues that excellent activity of the soul is intrinsically pleasurable (Nicomachean Ethics 1099a5).
If happiness is excellent activity of the soul, the latter is understood in relation to the human function.
