Both the NP and CNS have the following roles: clinician (practitioner), educator, collaborator/consultant/change agent, researcher, advocate. The roles may be given different titles, but the functions are basically the same. The difference between the NP and CNS rests on how these roles are enacted. The NP has a central role of clinician and the other roles are secondary. The NP performs all roles, but the role of clinician/practitioner is central to the NP practice. NP's are primary health care providers who diagnose illness, order, conduct, and interpret diagnostic and lab tests, prescribe medications (if authorized) and treatments. They provide health teaching and counsel patients.
The CNS uses the same roles, however, each role has the same level of importance and the practice involves focusing on one or more roles at the same time. For the CNS there is no role that more central to the others.
The topic of combining the 2 or keeping them separate is a hot topic in advance practice nursing. Some say the functions are more similar than different and the CNS and NP roles should be combined. Others hold that the functions are different and the CNS and NP roles should be kept separate.
This is just a brief explanation, some nurses have done entire dissertations on this topic.