Revisionism is not quite a straight-forward concept; it has a very complicated history, and it can take on very different meanings depending on the context. It has uses outside of history, as well, notably in historic Marxist political discourse. For historians, there are fundamentally two kinds of revisionist practice: one is a necessary and valued component of mainstream history, the other is a subversion of it.

Mainstream historical revisionism is the process by which historians inspect and question established orthodoxies in the historiography of a topic. Academic revision is an essential part of the process by which historical consensus if formed; revisionist historians offer interpretations of the past that challenge orthodox ones, but are rooted in a rigorous and sincere analysis of the evidence - both new evidence and a reinterpretation of existing evidence. Revisionists seek out new material, ask new questions of the existing material and question traditional methods and understandings, all out of an effort to construct a better history. Certain trends in historical practice lend themselves very easily to revisionism; womens history for instance very often demands a rejection or amendment of traditionally male-dominated narratives or interpretations of history. All of this is important to historians - much like the scientific community reruns experiments to test their validity and veracity, we reinterpret evidence and debate the merits and significance of those interpretations. When arguments posited by revisionists gain mainstream support and traction, they can become new orthodoxies. Generally speaking, we tend not to refer to this kind of history as revisionist because of the pejorative meaning attached to the term, but it is a kind of revisionism.

The other context in which we use the term historical revisionism - probably the more typical one - is when people set out to purposefully distort the historical record to advance an agenda. This kind of negative revisionism relies on the chronic misuse and misinterpretation of evidence, including the use of extremely dubious evidence (like contending obviously forged documents are authentic or being highly selective of evidence deployed). It often depends on inventing ludicrous reasons for rejecting the claims of mainstream history, and the manipulation of evidence and data, though these things can be presented in ways which are very convincing to the layman. It is in theory the same as the 'good' kind of historical revisionism in its goal; but it is the flawed methodology and dubious intentions that make it worthless. Holocaust denial is an example of one of the absolute worst kinds of historical revisionism, whereby people like David Irving have gone to extraordinary lengths to distort the historical record because they desperately don't want the holocaust to be true.

Whereas the good kind of revisionist wants to make our narrative of history fit the past, the bad kind wants to make the past fit their narrative instead. The good kind seeks out all relevant evidence first and makes an argument from it, with the historian being open to having their starting ideas challenged and shaped by what they encounter; the bad kind seeks out the evidence for an argument they have already decided on, and selectively rejects whatever does not fit that argument.

The bad kind of revisionism tends to end up being ridiculous by its nature. As historians, we are very open to accepting and critiquing new ideas, as long as we can see that they have been sincerely argued. Negative revisionism is almost always apparent as an attempt to impose ideological narrative on history. It naturally lends itself to conspiracy theory and extremist ideology. Bad revisionism is a key component of a lot of ridiculous popular history that flies around (like my old friend "white slavery" - oh what boundless joy it is to see the new and exciting ways people will butcher the historical record to back that one up), and is often the preserve of people who lack proper historical training - though plenty of mediocre work can slip through peer review, you aren't going to get your article on holocaust denial printed in Holocaust and Genocide Studies, but you might trick some popular press into publishing it.

However, it should be said that sometimes the line can blur - not all bad revisionist history is necessarily wholly worthless. In countries where the government has an interest in manipulating the historical record (e.g., the Soviet Union) for example, historians can obviously only work if their efforts are pleasing to the political orthodoxy; this can lead to work that blends both kinds of revisionism together. Unfortunately, in those circumstances you still have to be cautious and dubious about everything because it isn't easy determining where ideology and practice are intersecting, or how sincere that intersection is. More benignly, sometimes historians can have their work coloured by pre-conceived notions and values, particularly if they are exploring issues sensitive to them - they may at times push the credibility of their arguments a bit too far, or draw more than is entirely reasonable, from their evidence because they (perhaps without quite realising it) really want something to be the case. We generally distinguish this from true negative revisionism where there is a willful intent to serious distort the record, though we might make the critique that it tends dangerously close to it at times. Early critics of now-holocaust denier David Irving made this point in reviewing his books.

I just wanted to comment on one portion of your question:

Can you, without bias or judgment, and strictly sticking to the facts and objective differences

Nope. Bias can be minimized but not eliminated, and the same goes for judgement. I am inherently biased if only based on when and where I was born, what language(s) I speak, and the resources available to me. I was born in the US, raised Catholic, have some skill in Spanish but less in Italian and German, and have had a set of life experiences that differ from others in ways I understand and in ways that I don't comprehend. Were I born a decade earlier or a decade later, subtle things would influence my worldview. Stretch that timeline out further or transplant my birth and upbringing to another location and the differences would increase. Maybe I could read French in one of those scenarios, which I can't do now and that limits what sources I can access on papal diplomacy. If I were richer I would be camped out in Rome getting what I could out of the documents in the Vatican archives. Were I poorer I would likely have to work more and not be able to focus on history as much as I can right now. I can try to minimize these biases (and as a historian you are trained to do this), but they don't just disappear.

and strictly sticking to the facts and objective differences

This is influenced by all of the above, but it also is a difficult concept to achieve. Even facts are problematic. If we just take the facts about grain shipments in the Roman empire we could have dates and ships and tonnages, but even that neat table of facts can be lying to us. We might see a dip in deliveries, but what caused it? Was it pirates taking a few of the ships en route? Was the grain diverted to feed a military campaign or to counter a local drought? What do we do if our sources disagree as to the motivation behind the shipments dropping off for a time? Is one of them lying, or mistaken, or something else? We have to look at the evidence (and realize that what evidence we have is limited and what those limits might be) and then use our judgement to make an argument. Or perhaps we might look at "objective differences" between one set of census data and another, but if we just looked at the numbers we would be missing a discussion about how the questions or questioners display bias themselves.

The facts are important--even vital. But history lives in the interpretation of those facts. And revision of earlier interpretations can be incredibly useful--or harmful--as well. So in your example, Zinn is useful as a corrective to some earlier historical narratives because those arguments were flawed in some ways, but he introduces a number of problems at the same time due to his own biases. That doesn't mean that we throw away his work or the work of the people he was arguing against or that we just throw up our hands and give up. What it means is that we need to critically engage with our sources (both primary and secondary) and do our best to exercise sound judgement.

To tie this in with your overall question, even in this post of mine where I tried to stick as closely as possible to the facts I think that understanding the reality of the situation is harmed by only sticking to the bullet points and tables while skipping the rest of the text. My post is "revisionist" in that it seeks to counter the narrative that the British were losing the Battle of Britain until the Luftwaffe switched targets to British cities. It uses the existing facts as well as some sources that only became available well after the war was concluded. Mine isn't a novel argument (evidenced by my citation of Hastings), but it is revisionist in a sense when contrasted with earlier narratives (from both historians and from contemporary accounts like that famously constructed by Churchill himself).

/u/sowser already covered how revisionist history can be useful or damaging (and they did so in excellent fashion, I must say), and I hope my Battle of Britain post sits more in the former category than the latter. Where it sits is up for you to judge. Evaluate my claims. Look up what others claim. See if the sources used line up better with one narrative than another and see what makes sense. Maybe it's mine, maybe it's someone else's, or maybe all of us are missing something and you can construct a narrative that you think is more compelling. If you did, you would be a revisionist historian--and you would hopefully have added to our understanding of the subject and its historiography.

Just as a supplement to the posts answering your main question, if you are specifically interested in Howard Zimm, you might be interested in this 2 year old thread

hi! I'll leave this for the experts, but meanwhile, you may be interested in this recent-ish post, which includes links to several more

• Why is the label "revisionist" so charged with disdain and discredit?

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