Master degree after PhD?

There's someone on the masters course I'm about to start who already has a PhD in another subject,so yes it can be done. I can't see the point in doing one in a closely related subject though - I'd guess the main motivations would be either out of interest (if you have the time and money to spare) or as a step to a career change.

My MA supervisor was doing an MA at the time - in a related field, but different enough to warrant it, as she wanted to shift her research focus.

I also know someone who went back several (i.e. A LOT) of years after their science PhD to do a humanities research MA. It was after they retired though, and just for fun.

I've considered doing another Master's after I've finished my PhD, but it wouldn't be for several years.