I recently read two very interesting (and very different articles) that made me think about how preconceptions influence historical writing.
The first article was a review of Niall Ferguson's book, The Pity of War by Jay Winter. Winter argued that Ferguson brought his politics to the study of war, using counter-factual history to support his arguments. For example, Ferguson argued that had the British not entered WWI, there is 'no question' that the Germans would have won the war. Ferguson also claimed that WWI was 'the greatest error of modern history', because its ultimate aim, to end German dominance of Europe, has failed anyway, as Germany now dominates Europe (although economically, not militarily). Ferguson also claimed that the British sacrificed their empire status thanks to the war, and that Britain squandered her assets and manpower on an avoidable and pointless conflict that ultimately led to the decline of the British Empire. Winter disagrees with Ferguson, arguing that there are so many variables that make up history that it is impossible to specify which exact variable caused a consequence, and for example, what exact variable caused the Germans to lose WWI (British entry, the strength of their army, their military planning etc.).
The second article, Making and Eating Ice Cream in Naples: Rethinking Consumption and Sociability in the Eighteenth Century by Melissa Calaresu shows how northern European historians have mistakenly assumed that ice cream must have been a food for the rich because, firstly, they were unaware of the snow trade and secondly, because sources tend to be biased towards the rich (for example cook books for stewards of large houses). This means that historians tend to only have sources of ice cream being served at aristocratic banquets in Naples, and have few sources of it being eaten in coffee and ice cream shops and being sold on the street and made in modest households. Because northern European historians saw how expensive ice was in northern Europe at the time, they wrongly assumed that the same was in Naples, meaning they assumed that ice cream was an expensive treat. In reality there was a snow trade in Naples that meant anyone, from a child on the street to a rich aristocrat, could buy it as long as they had a few coins to spare.
What the two articles show is how historians can often be mistakenly blind sided by preconceptions when looking at evidence, and how important it is for a historian to look at sources from a totally fresh point of view, forgetting the assumptions and prior knowledge they have (or think they have), which may influence their interpretation of sources.