The essential difference between an affidavit and an oath is that one is a statement and the other is a promise. A document which is a written, sworn statement of facts regarding a particular issue is called an affidavit, and an oath is a promise to perform a specified duty such as telling the truth. Swearing or affirming an oath that the facts contained in the document are true is a vital part of an affidavit. The oath is what makes the affidavit the equivalent of legal testimony in a court of law. The affidavit is not considered valid without the oath; however, oaths also have many other applications.
An affidavit can take the place of live testimony in court proceedings for a variety of reasons, such as a witness moving or being too ill to appear in court. It can also be used in minor proceedings such as motions and hearings as a statement of the facts involved that may not require personally appearing in court. When live testimony is given, the witness swears an oath to tell the truth in front of the court. Since an affidavit is accepted as testimony in a range of legal matters, the witness who is also called an affiant is also required to swear an oath in front of a person with legal authority such as a notary or other judicial officer.
When preparing an affidavit, a person typically writes down all of the relevant facts concerning the legal matter. He or she then reports to a notary or other legal officer with the affidavit and an oath is administered. The person must swear an oath that the information contained in the affidavit is true to the best of his or her knowledge. Once this is done, the notary certifies that the witness appeared with the affidavit and an oath was sworn in his or her presence in a special section of the document called a jurat. The jurat also states when and where the oath was sworn and who administered it.
An affidavit required an oath in order to be considered valid testimony in a court of law or as a legally binding document any other purpose. Oaths are also used in a variety of other ways, often in situations where a person needs to promise to perform a specific duty before God and witnesses. Some examples of this are as to tell the truth, to uphold the law, and to perform a job to the best of their ability. Government officials swear an oath of office, promising to perform the duties of the office and uphold the laws of the land. Doctors take the Hippocratic Oath, swearing to provide medical care for patients and to do no harm in the course of their professional duties.