I'm not sure you can have hard SF without hard science. :P

The soft sciences certainly have SF based around them (the 'New Wave' movement is based around psychology, sociology, anthropology etc) but the lack of general agreement in these fields means that there can't really be a 'scientifically accurate' depiction.

Asimov's Foundation would be an example of SF based on sociology (even if he calls it psychohistory), but the mathematical aspect makes it unconvincing.