The classic definition of history is the study of change over time. It is now, however, as many consider it, a simple matter of facts and dates. Daniel Boorstin once said, "Our past is only a little less uncertain than our future." We are limited in our understanding of the past by the imperfect record that has been left for us. A history text is like a family album--it doesn't tell the whole story. So, perhaps a more accurate definition would be "the interpretation of events of the past and how they have affected change over time." The historian is at once an iconoclast--who challenges and sometimes destroys cherished images of the past; and an inquisitor; who pursues the truth of that past relentlessly. Frank Luttner, in The Devil, History, and Studia Humanitatis put it this way:
Historians are curious creatures. They estimate it a stroke of good fortune to find something from a distant culture that makes no sense. That which cannot be explained becomes a clue to a different way of thinking. It becomes a riddle to be solved, the more difficult, the more illogical, the more extreme, the more comical, the better. It becomes an invitation for the historian to reconstruct the original assumptions beliefs, perceptions and anxieties; to see through the eyes, feel from the hearts, and reason from the minds of people who lived in distant times and places. In the process, the historian recovers a piece of humanity, another way in which humans have experienced and understood their condition
To know what history is, consider the following quotes that come from the hnn.us link below.
Napoleon has a famous quote about history. It is given in this link as
History is a myth that men agree to believe.
What this tells us is that history is not some set of objective facts about things that have occurred in the past. Of course, there are objective facts about history. Japan did attack Pearl Harbor on Dec 7, 1941, for example. But just knowing that date is not what history is.
History is about why things happen. The previous answer quoted Santayana's saying about needing to learn the lessons of history. History's lessons are not about what happened (WWII happened) but about why they happened. It's important to know why bad stuff happened so as to prevent it.
But this is where the difficulty comes in. The "why" of things is not objectively knowable. Why did Japan attack Pearl Harbor? Were they greedy or was the US unreasonable and applying a racist double standard to expansion and empire? The answer to that is whatever "men agree to believe."
This subjectivity is why another quote from the link makes sense. This quote says
God alone knows the future, but only an historian can alter the past.
Historians constantly alter the past by reinterpreting it. Sometimes this is based on new knowledge, but often it's based on new opinions -- on new "myths" that "men agree to believe."
So... one final quote
History consists of a series of accumulated imaginative inventions.
History is what we imagine it to be. It is a set of subjective myths that only become "truth" when we agree that they are true. Therefore, history can be changed and history is, ultimately, impossible to know on an objective basis.
This is a fascinating question. The role of history, and the consequent function of the historian, are both elements that can be subject to wide interpretation. One line of logic suggests that the history discipline allows individuals to gain a better understanding of the past in order to avoid past mistakes. In this light, history is a self- correcting mechanism. When Santayana argues "Those who cannot remember the past are condemned to repeat it," it brings to light one of the foundational beliefs about history. The discipline and those who study it might possess a belief that there is some connection or pattern between what has been done in the past to what is being done now or can be done in the future. In this light, history reveals these connections. On another side of the coin, some believe that history's greatest attribute is the recreation of past events, without a sense of judgment. This recreation makes history as technical as a science and the historian a form of the scientist, painstaking in both pursuits of recreating and collecting data from other time periods.