I'm tempted to recommend first that, if you haven't already done so, you take a look at Plato's dialogue *Meno*. That dialogue raises all sorts of issues about what virtue is, and how we should best go about understanding it. The view Socrates takes there seems to be that there is some single property, essential to all virtues, that makes them virtues, and that if we could grasp that property then we'd be in a position to decide whether some alleged virtue (such as those in your list) really is a virtue. Against that, you might want to look at what seems to be the anti-essentialism of Wittgenstein (see e.g. his *Philosophical Investigations*, esp. sects. 65-77). On this view, the claim would be that we group the different virtues together because they bear 'family resemblances' to one another. So the concept, to use another of Wittgenstein's metaphors, is like a rope, but with no single strand running through all of it.

Let's say, taking a leaf out of Aristotle's book *The Nicomachean Ethics* book 2, that a virtue is a disposition of a person, to act and to feel in certain ways. And presumably we want to say that these ways are in some way morally admirable (so someone might doubt your suggestion that strength is a virtue in the usual sense). How do we decide which dispositions constitute virtues and which don't?

Well, we are now in the thick of moral philosophy. One answer, which has become influential in recent years, is again Aristotelian. A virtue is a disposition that enables its possessor to flourish in some way. But it has to be said that in Aristotle's own view the notion of flourishing is made to overlap uncomfortably closely with that of what is morally admirable (so you flourish even if you are killed at a young age in battle, because flourishing consists in exercising the virtues -- see book 9, ch. 8). And without that overlap, the position ends up looking rather like egoism -- the view that you should do what's best for you, regardless of others.

Another position, which you'll find in David Hume (see his *Enquiry concerning the Principles of Morals*), is that the virtues are those dispositions that will overall do the most good in society. So for Hume there is no virtue in e.g. asceticism, and the key virtue is benevolence.

Myself I prefer Hume to Aristotle on this issue, and I think he probably deserves more attention than he's been getting from philosophers interested in the virtues.