Full Idea
If you found that I had the same car as you, I don't suppose you would care, but if you found I had the same fiancée as you, you might not be so happy.
Gist of Idea
'I have the same car as you' is fine; 'I have the same fiancée as you' is not so good
Source
J Baggini / PS Fosl (The Philosopher's Toolkit [2003], §4.17)
Book Reference
Baggini,J and Fosl,P.S.: 'The Philosopher's Toolkit' [Blackwells 2003], p.171
A Reaction
A very nice illustration of the ambiguity of "same", and hence of identity. 'I had the same thought as you'. 'I have the same DNA as you'.