Inherent authority, also called "inherent agency power" is a type of authority described in the Second Restatement of Agency that is distinct from acutal authority, apparent authority, and estoppel, and is derived "solely from the agency relation and exists for the proection of persons harmed by or dealing wtih a servant or other agent."
The concept of inherent authority is often difficult to distinguish from apparent authority. Indeed, the Third Restatement dispenses with the concept of inherent authority, saying that all such authority is contained within actual authority, apparent authority and estoppel. The concept of inherent authority has been used in situations where the principal has not made any "manifestations" to the third party, but the third party has reasonably relied on the agent's authority. Because manifestations of the principal are a requirement for creating apparent authority, such situations would not traditionally fall in the apparent authority category.
One concrete example of a situation where inherent authority has significance independent of apparent authority is in the undisclosed principal situation. An agent for an undisclosed principal cannot have apparent authority because the third party has no notice the agent is acting for a principal. Thus, inherent authority can be helpful when an agent acts on behalf of an undisclosed principal without actual authority. The Third Restatement effectively preserves this outcome without using the concept of inherent agency under the rules about undisclosed principals in 2.06(2).
The concept of inherent authority is sometimes thought of as the contractual equivalent of respondeat superior in tort. Just as an employer is liable for the torts of employees within the scope of their employment, the thought is that principals should be liable for the contracts made by their agents, whether or not actual or apparent authority is present. Most courts, however, have not expanded the concept of inherent authority this far.