Because hadith were passed down orally and not compiled in written works until around the third century of Islam, there is no ancient written documentation to examine. Thus, according to the classical science of hadith, there are three primary ways to determine the authenticity ("sihha") of a hadith: by attempting to determine whether there are "other identical reports from other transmitters"; determining the reliability of the transmitters of the report; and "the continuity of the chain of transmission" of the hadith.