Any individual can offer an affidavit as long as they have the mental capacity to undertake the oath of their own free will. Affidavits are understood to reflect the personal knowledge of the individual providing the oath. This means that the individual providing the statement is not held liable for information of which they were not personally aware.
It also means that the statement may include personal beliefs or opinions in place of, or alongside, fact. In these instances, statements of belief or opinion will need to be clearly stated as such in the affidavit.
Under certain circumstances, an affidavidt may provided by a guardian on behalf of an individual who is mentally incapacitated.