General vs. Specific
A general power of attorney grants the agent the authority to perform any legal act that the principal is entitled to perform. He may sell the principal's house, for example, sign contracts that bind the principal or make medical decisions on behalf of the principal. Because of the broad grant of authority, general powers of attorney are seldom used. A specific power of attorney grants the agent the authority to perform a specific legal act or a narrow range of legal acts on behalf of the principal. The agent may, for example, be granted the authority to make medical decisions on behalf of the principal or to sell the principal's house while the principal is overseas.
Three types of powers of attorney are commonly used -- durable, temporary and springing. The authority granted under a durable power of attorney endures until the principal either dies or revokes the power of attorney. A temporary power of attorney endures until a certain date authorized by the principal or until a particular event (such a the sale of a house) is accomplished. A springing power of attorney takes effect upon the occurrence of a particular condition -- such as the mental incapacity of the principal -- and endures until the condition caused by the event no longer exists.
The principal may revoke a power of attorney at any time by delivering written notice of revocation to the agent. The only circumstances in which a principal would not be entitled to revoke a power of attorney are mental incompetence and inability to communicate (as in the case of a serious illness).
Even after a power of attorney is revoked, the agent may still have the power to bind the principal to transactions entered into by the agent in the principal's name. An agent may, for example, present the power of attorney form to a seller of real estate and sign a real estate purchase contract in the principal's name. The principal would be bound to purchase the real estate despite having already revoked the agent's authority, if the power of attorney form appeared to be valid and the seller had no reason to know that the agent's authority had been revoked. In such a case, the principal would have the right to sue the agent for damages but could not escape the obligations imposed by the real estate purchase contract.