Abductive reasoning or abduction infers unseen facts, events, or causes in the past from clues or facts in the present. It is a type of reasoning used by historical scientists when they reason from clues back to causes. The American philosopher and logician Charles Sanders Peirce was the first to describe it. As he noted, the problem with abductive reasoning is that there is often more than one cause that can explain the same effect. He suggested that a particular abductive hypothesis can be firmly established if it can be shown that it represents the best or only explanation of the "manifest effects" in question.