About a generation after Herodotus, Thucydides wrote an account of the Peloponnesian wars and was more precise in his use of evidence and analysis. He insisted that history had to be backed up with more relevant evidence and facts. Greek historians interpreted records with too much credulity and little skepticism. Many pre-nineteenth-century historians handled evidence with a casual disregard for critical standards. They did not understand that with time, values and standards were changing. With that in mind, modern historians started to disbelief past historians due to no primary sources and no way of knowing what was true. Voltaire, in the eighteenth century, dismissed the Middle Ages as unworthy of study because medieval men and women were not "enlightened," as he felt himself to be (HP4).
History became more academically during the French revolution, people became more "history-conscious" than ever before. German historian Leopold von Ranke played a leading role in establishing history as a respected discipline in the universities. He firmly established that history must be backed up with primary sources, in other words they couldn't use God as form of evidence. Von Rank rejected ethnocentrism and was for presentism, which is when someone studies the history of the past they need to have the mindset of not the present but of the point in history of what is being studied. Von Ranke popularized the idea that history should be studied similar to science, not in the case of discovering general laws but in the way that scientist prove there facts and are based on critical standards. Ranke, then, and many other eminent scholars, established the study of history on a firm methodological foundation (5).
Von Ranke thought it was crucial to back up his ideas with proven facts and reliable evidence. Ranke was a positivist and an empiricist. Positivism is a philosophical system that holds that every rational justifiable assertion can be scientifically verified or is capable of logical or mathematical proof.