An evidentiary privilege is a rule of evidence that allows the holder of the privilege to refuse to provide evidence about a certain subject or to bar such evidence from being disclosed or used in a judicial or other proceeding. One well known privilege is the solicitor–client privilege, referred to as the attorney–client privilege in the United States and as the legal professional privilege in Australia. This protects confidential communications between a client and his or her legal adviser for the dominant purpose of legal advice. The rationale is that clients ought to be able to communicate freely with their lawyers, in order to facilitate the proper functioning of the legal system. Other common forms include privilege against self-incrimination (in other proceedings), without prejudice privilege (protecting communications made in the course of negotiations to settle a legal dispute), public interest privilege (formerly Crown privilege, protecting documents for which secrecy is necessary for the proper functioning of government), marital privilege, medical professional privilege, and clergy–penitent privilege. The effect of the privilege is usually a right on the part of a party to a case, allowing him to prevent evidence from being introduced in the form of testimony from the person to whom the privilege runs. For example, a person can generally prevent his or her attorney from testifying about the legal relationship between attorney and client, even if the attorney were willing to do so. In a few instances, such as the marital privilege, the privilege is a right held by the potential witness. Thus, if a wife wishes to testify against her husband, she may do so even if he opposes this testimony; however, the wife has the privilege of refusing to testify even if the husband wishes her to do so.