The social psychologists John French and Bertram Raven (1958) identified five bases of power:

• Legitimate power – stemming from a belief that a person has a right to exercise power based on their status or position.
• Reward power – stemming from an individual’s ability to provide rewards or compensation.
• Expert power – based on knowledge held by an individual as a result of their skills, knowledge or experience.
• Referent power – based on personable qualities such as charisma and attractiveness.
• Coercive power – stemming from an individual’s ability to punish or impose sanctions.

(Source: The Open University, 2012).

It appears to me that the most effective modern managers must attempt to make use of a combination of referent and expert power, perhaps backed up by some legitimate power, and maybe some reward power too. Coercive power seems like a last resort.

Update:

Raven (2008) subsequently added a sixth basis of power, which is potentially one of the most desirable types of power:

• Informational power – stemming from an individual’s control over access to, or of quality of, information. Informational power can be as simple as telling someone how to do something, and in so doing their subsequent behaviour changes.