When historians analyze the source they use to write and develop a historical theme, event or process, they try to remain objective. This is not easy to achieve, since historically sources should be explored to judge to what extent this source is objective, when it was written, who wrote it, under what conditions and in what kind of environment. All this in order that the analysis and implementation of the given source in the work of the historians will be representative and accurate, in other words to avoid bias, ie they want to be unbiased by personal feelings and opinions.