Also note that I have never watched Human Nature/Family of Blood at the time of typing this. I may edit it if/when I do. I have read the script!
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My principal of the Chameleon Arch is this -- when it comes down it, the formula for a Time Lord is:
You could get more complicated (if you want to be real specific, the formula as I believe it should be (past regenerations)(current regenerations)(culture) = personality; (culture)(memory) + biology = time lord but this is why I don't do meta after algebra) but that basically covers it. Culture counts in with memory; what is culture but shared communal memories and behaviors? (I'm sure some psychiatrist is rolling in his grave at my awkward phrasing, but.)
To be even more simple about it?
Memory defines who you are
Which could just be said to be a univeral truth, in my opinion. But the reason we need the formula is because when it comes to the Chameleon Arch, it rewrites not only what you are, but to some degree, who you are.
( Rambles like mad under here. )