Where are you headed? Denison Beach, Tasmania's East Coast. January 2013. It is Theme Thursday and there seems to be some complexity about the spelling of 'COMPLEXITY'S'. It would seem to me that complexity would only become COMPLEXITY'S in the context of the marking of possessive case (i.e. "for COMPLEXITY'S sake, the apostrophe can be useful".) If we're not talking about the possessive, and purely the plural, 'ies' comes into play (i.e. "there are many complexities in the world of grammar"). Perhaps the use of the possessive is deliberate, and I have a cheek to even raise it. In which case, I apologise. Carry on!