The philosopher’s axe is a nice shorthand for an important idea.
The axe has been in the family for generations, in constant use for wood chopping. Over time, the handle falls off and has to be replaced, and then again, and then the head wears out and needs replacing. It’s been used all that time, but the question is, is it still the same axe?

So, the Sugababes.
No, this isn’t a subject change.

It’s just been announced (via Twitter and the band’s website of course – this is the 21st century) that Keisha Buchanan, the last founding member of the Sugababes has left the group.
Here’s the BBC’s coverage
But leaving aside the who-said-or-did-what-upsetting-whom stuff, look at the band line up.

In 1998, Keisha Buchanan, Mutya Buena and Siobhan Donaghy formed the Sugababes (they were not a manufactured group, hence the stupid, teenagey name).
Siobhan left in 2001, replaced by Heidi Range (formerly of Atomic Kitten). Mutya left in 2005 and was replaced by Amelle Berrabah. And now Keisha’s left too – to be replaced by Jade Ewen.
Jade was the UK’s 2009 Eurovision entrant – it’s all getting a bit like football transfers, isn’t it?

So who are the Sugababes?
Are they the singers (although none of the original three are now in the line-up)?
Are they the songs and the back catalogue (most of which were written by the band members and from which presumably they’ll continue to get royalties)?
And if you see the new line-up performing songs from before Heidi joined, are you in fact watching a tribute band?