When are 2 PhDs in philosophy necessary? I stumbled on Tom Angier on his UCT page, but this page details his degrees more:


  MPhil. in Philosophy (University College London, 1995), PhD in Philosophy (University of Cambridge, 2001),
  PhD in Ancient Philosophy (University of Toronto, 2008).



I grasp that a braggart may like the cachet  of having 2 PhDs. But I'll assume that there are other modest reasons. 
Couldn't Dr. Angier have studied in Cambridge, whatever he studied in Toronto, by taking more time in Cambridge? 
In general, why'd you need 2 Philosophy PhDs?
Just reading the two titles, those PhD's each have a different focus.

I assume that the Cambridge PhD is "modern"...
And the Toronto one is prior to some defined date.

This means that Tom decided to augment or broaden his knowledge, perhaps due to interests gained in the first PhD. I'm guessing - only he knows why for sure.