The discussion of snake's sentience reminded me of an argument I once made about the nature of pureblood discrimination against Muggles, which I'll reproduce here:
Consider how we, as humans, justify our definitions of personhood. Why do we say that chimps, for example, are not people? Essentially, we come up with a list of features which we have, and things which aren’t people don’t have, like talking, tool use, etc. and then say everything which looks very similar to something which has those features is a person (why, for example, we consider a severely mentally retarded person a person).
In the Wizarding World, manufacturing a facsimile of sentience – talking, etc. is trivial. Even a very poor family can purchase multiple such objects as a child’s toy (Magical Chessmen). They would reject that these object are people, they’re simply toys, not truly free willed, despite resembling that strongly. When it comes down to it, the only difference between real people and all these simulacra seems to be the ability for autonomous magic use – so this becomes the criteria for person-hood.
For wizards, form is not a determinant of nature, thanks to the various transmutations and shapeshifting that is possible, this means that something looking similar to a person cannot be assumed to have the characteristics of a person, so the familiarity based extension I mention above that we have doesn’t apply.
All in all, by this rather natural definition, Muggles aren’t people. All they are is clever simulacra, with no greater moral significance than a child’s toy.
Move back to the chimp analogy. A chimp can do many things a person can do, but falls short on the key criteria. Despite this it’s being suggested that human-chimp hybrids may be genetically viable. It’s quite possible such a hybrid would then meet the criteria for personhood by our definition. Would you approve of people breeding with chimps? Or accept chimp-human hybrids as full members of society without reservation?
I actually rather like the canon Ministry of Magic's current definition of personhood, which is "any creature that has sufficient intelligence to understand the laws of the magical community and to bear part of the responsibility in shaping those laws".
Further, certain intelligent creatures such as centaurs have declined legal personhood status in favor of self-governance.
[Update: and now there's a fifth discussion thread, which you should probably use in preference to this one. Later update: and a sixth -- in the discussion section, which is where these threads are living for now on. Also: tag for HP threads in the main section, and tag for HP threads in the discussion section.]
The third discussion thread is above 500 comments now, just like the others, so it's time for a new one. Predecessors: one, two, three. For anyone who's been on Mars and doesn't know what this is about: it's Eliezer's remarkable Harry Potter fanfic.
Spoiler warning and helpful suggestion (copied from those in the earlier threads):
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.