A history book written hundreds of years ago contains several inconsistencies. Some scholars argue that because the book contains inconsistencies, the author must have been getting information from more than one source. The conclusion cited does not follow unless ["the history book's author used no source that contained inconsistencies repeated in the history book", 'the author of the history book was familiar with all of the available source material that was relevant to the history book', 'the inconsistencies would be apparent to the average reader of the history book at the present time', 'the author of the history book was aware of the kinds of inconsistencies that can arise when multiple sources are consulted']