What essential agreement assures that a lawyer can act on behalf of a client?

The essential agreement that assures a lawyer can act on behalf of a client is a retainer. This is an agreement between the lawyer and the client that establishes the terms of the legal representation and outlines the scope of the services to be provided. It serves as a formal contract which enables the lawyer to represent the client in legal matters, and it typically includes details regarding fees and responsibilities.

While "consent" is important in the context of legal representation, such as obtaining permission for certain actions or decisions, it does not serve as the primary mechanism for establishing the lawyer-client relationship. Consent is often part of the broader context of the retainer agreement but alone does not fulfill the need for a structured basis of representation.

Other options like "contract" and "affidavit" do not specifically address the lawyer-client relationship in the same manner as a retainer. A contract may encompass various agreements, but a retainer is specifically tailored to legal services. An affidavit, on the other hand, is a sworn statement used as evidence in court, and it does not pertain to the authority of the lawyer in representing the client. Thus, a retainer is the key document that solidifies the legal relationship between the client and the lawyer, affirming