source whose account can be confirmed by reference to outside authorities in some of its parts can be trusted in its entirety if it is impossible similarly to confirm the entire text. When two sources disagree on a particular point, the historian will prefer the source with most "authority"—that is the source created by the expert or by the eyewitness. Eyewitnesses are, in general, to be preferred especially in circumstances where the ordinary observer could have accurately reported what transpired and, more specifically, when they deal with facts known by most contemporaries. If two independently created sources agree on a matter, the reliability of each is measurably enhanced. When two sources disagree and there is no other means of evaluation, then historians take the source which seems to accord best with common sense. Subsequent descriptions of historical method, outlined below, have attempted to overcome the credulity built into the first step formulated by the nineteenth century historiographers by stating principles not merely by which different reports can be harmonized but instead by which a statement found in a source may be considered to be unreliable or reliable as it stands on its own. Core principles for determining reliability The following core principles of source criticism were formulated by two Scandinavian historians, Olden-Jørgensen (1998) and Thurén Torsten (1997): Human sources may be relics such as a fingerprint; or narratives such as a statement or a letter. Relics are more credible sources than narratives. Any given source may be forged or corrupted. Strong indications of the originality of the source increase its reliability. The closer a source is to the event which it purports to describe, the more one can trust it to give an accurate historical description of what actually happened. An eyewitness is more reliable than testimony at second hand, which is more reliable than hearsay at further remove, and so on. If a number of independent sources contain the same message, the credibility of the message is strongly increased. The tendency of a source is its motivation for providing some kind of bias. Tendencies should be minimized or supplemented with opposite motivations. If it can be demonstrated that the witness or source has no direct interest in creating bias then the credibility of the message is increased. Eyewitness evidence R. J. Shafer offers this checklist for evaluating eyewitness testimony: Is the real meaning of the statement different from its