Does "define an individual" mean "determine the essential quality of an individual"?
Background info:
Saks lives with
http://en.wikipedia.org/wiki/Schizophrenia and has written about her experience with the illness in her award-winning best-selling autobiography,
The Center Cannot Hold: My Journey Through Madness published by Hyperion Books in 2007.
http://en.wikipedia.org/wiki/Elyn_Saks#cite_note-6 Saks is also a cancer survivor. She emphasizes that "illness of any kind need not
define an individual, while remarking on the different ways that mental and physical illnesses are regarded".
http://en.wikipedia.org/wiki/Elyn_Saks#cite_note-saks25-7