Scientists also do not see the changes of facts and concepts that had happened in their discipline. Since they perceive the world differently than their predecessors and they think on the basis of different assumptions, they are not able to understand the meanings of words from old texts. They do not know that in the past one not so much thought differently (for incorrectly) about what they now think about, and perceived differently (for incorrectly) what they perceive, as one thought of and perceived something else. They instinctively understand old books and papers according to their own thought style and consider those texts as steps—although sometimes erroneous—towards this world-view which they possess now.