Under what condition may a lawyer represent a client against a former client?

A lawyer may represent a client against a former client provided that the former client gives informed consent. This principle is grounded in the ethical obligation to maintain the confidentiality of information obtained during the attorney-client relationship. When a lawyer has previously represented a client, they have a duty to protect that client's confidences and secrets. If the lawyer wishes to undertake representation against this former client, they must ensure that the former client fully understands the implications of this new representation and voluntarily agrees to it.

This requirement for informed consent helps to maintain trust in the attorney-client relationship and safeguards any sensitive information that may impact the former client. It also aligns with the broader ethical standards designed to prevent any potential conflicts of interest and the misuse of privileged information.

While other conditions or scenarios, such as the elapsed time since representation or the relationship of the new case to the previous one, may inform discussions about conflicts of interest, these do not provide a complete legal or ethical avenue for representation without the former client’s consent. Thus, informed consent remains the correct and necessary condition for a lawyer to ethically represent a new client against a former one.