Talking about property rights, Chris refers to one common justification for property: namely, that 'creating something generates rights over it'. There's no doubt that it's a widely shared moral intuition. If I fashion an old piece of wood into an intricate sculpture, whose should the sculpture be but mine? If you spend long days writing a literary masterpiece, are you not a proper beneficiary of its publication and sale?
What is less clear is why we think the creation of the object generates an entitlement on the part of its creator. Is this because it's he or she that's put in the effort, and so deserves the reward? Or is it because, independently of how much effort has been expended, something of the person is thought to be, loosely, 'in' the object created? Neither answer is unproblematic in its implications.
To take the second one first. John Locke gave it expression by writing of people mixing their labour with things to transform them, thereby joining to these things something of their own. In truth, though, if I make a sculpture it's not really like my mixing something of mine into something else: some salt, say, that I've bought in the supermarket and dropped into a puddle of water in the road. 'Mixing my labour' with the wood is just a metaphorical way of presenting what has happened. Even if the analogy were exact, a question asked by Robert Nozick (and altered to fit my example) kicks in here: why should I gain the puddle, rather than lose the salt? Furthermore, there's a question about boundaries that goes to the heart of what's troublesome about entitlements based purely on creating something. If I step off a boat on to a previously uninhabited island or, better still, continent, and turn over a spadeful of earth, does this give me rights to the entire land mass? If I surprise an unowned herd of deer and cause a change in their pre-enounter-with-me condition, do I now own the herd?
Scepticism towards the moral robustness of an affirmative answer to these questions, of property rights resting on an entitlement to the 'fruits of one's labour', may suggest that the real principle at work is, rather, one of reward-for-effort. I made the sculpture and it cost me time and energy to do so - that's why it's mine. The same argument doesn't work in the case of my surprising the herd or altering a tiny bit of the face of that newly-found continent. However, once ownership is to be decided on the basis of desert, things become more complicated. For there are different bases of desert than merely effort, and there are other reasons for assigning things to people than merely desert - need being one of these. And should two people who have to expend different amounts of effort to achieve the same result be rewarded differently?