premise: Edward Gibbon FRS ( ; 8 May 173716 January 1794) was an English historian, writer and Member of Parliament. His most important work, "The History of the Decline and Fall of the Roman Empire", was published in six volumes between 1776 and 1788 and is known for the quality and irony of its prose, its use of primary sources, and its open criticism of organised religion.
hypothesis: "The History of the Decline and Fall of the Roman Empire" had six volumes published in four years.
reason: "The History of the Decline and Fall of the Roman Empire" had six volumes published between 1776 and 1788, which is more than four years. I think the AI is confused by the way that it is worded and that maybe it can't decipher how many years are between those dates.