All primary sources require criticism: nothing should be trusted at face value. Insights about the past based on oral histories or on how a group of people remember past events require their own sort of source criticism. Many historians would see the evaluation for these sorts of sources as being necessarily more rigorous, but we should keep in mind that any written source can be flawed as well. Nothing should be accepted on face value.

Some historians place more of a premium on the folk memory of the past, evaluating it as a source of perspective rather than as a source of verifiable information. The folk memory of the Kennedy assassination can be a fascinating subject, but it is a step removed from delving into the question of who actually fired the bullets.

I would see "folk memory" as distinct from "popular history," if the latter is used in the context of a history of what everyday people were doing - of what they wore, what toys they bought for their children, what music they listened to, etc.

Despite /u/jschooltiger having summoned me, I may not be the best person to answer this. I would be interested to see how others might address this subject.

^(Please note I've moved my account to /u/Bealoideas, so if you have any further questions on this topic, I would be happy to answer messages sent there.)

Folklorists are usually experts on the meta-study of folklore, rather unfortunately I don't fall into that generalization but nonetheless I can tell you, within my own field unequivocally yes. Folklore is not particularly interested in historical truth (I'd argue it doesn't exist in fact), rather with what people believed or did; and the study of folk memory falls very much into this line of thinking. In a broad sense, if you were to study history through only the strictest official channels, you may end up with a very divergent viewpoint of the period as compared to what contemporary people thought.

Rather than give a whole diatribe on folklore and its study, let me give you an example of the value of studying folk memory. You'll have to bear with the diversion to my own area of study, but I hope it will serve as illumination. If anyone is not interested in this case-study they can skip the remainder of this comment, as /u/GaiusPlinius raises some additional questions below.

So in Ireland, a country with a very rich folk tradition and oral culture, by far the figure who is most represented in modern folk tradition is Dónall Ó Conaill, better known in English as Daniel O'Connell. Ó Conaill is a celebrated figure for his role in the campaign for Catholic Emancipation, which is rather a complex subject to get into, but for brevities sake he was a champion of the underclass at the time. A truly larger than life figure, he is remembered in official historical terms as The Liberator and The Emancipator.

Now a historical analysis of a man like Ó Conaill might lead one to believe that these reforms he championed, which would liberate the very people who would form the oral tradition surrounding him, would figure prominently in the folk memory itself. In fact the opposite is true: Ó Conaill is never referred to as The Liberator or The Emancipator in the oral tradition, and his role in Catholic Emancipation doesn't figure into it at all! Rather in the folk memory he is called The Counselor, and the stories told of him in the oral tradition revolve around fantastical (and wholly fictional) legal exploits, which demonstrate his cunning and guile as a lawyer. A popular version of a story has Ó Conaill, trying a case before a corrupt member of the establishment upper class, entraps the man during the proceedings, either with some clever legal wordplay or some other canny scheme. This is actually quite a common characteristic of folk tradition in Ireland, also apparent with figures like Fionn mac Cumhaill - where cleverness and guile are often valued above other virtues.

In other cases the folk memory of an otherwise well-studied historical event, can provide valuable cultural information about the social fabric at the time. To make use of Ó Conaill's history once more, he famously fought a duel against a member of the Dublin Corporation, one John Norcot d'Esterre, on February 1st 1815. Ó Conaill had publicly called the Corporation 'beggarly', and d'Esterre - who was insolvent at the time - took personal offense and challenged him. D'Esterre was very much a member of the Protestant establishment, and a perfect villain (in the public mind) to oppose the enormously popular Ó Conaill.

Rather unfortunately for d'Esterre, who was extremely nervous about the whole thing and was probably strongly pressured into it, Ó Conaill was something of crack-shot, and wounded him in the groin during the duel - whereafter he died three days later in some misery. Now, the effect of the duel and its outcome are well attested by the historical record - Ó Conaill was said to be deeply troubled by the events, and claimed that it haunted him for the rest of his life.

However unlike the famous American Burr-Hamilton duel of only a decade prior where fewer than ten men were witness to the event, evidently here a ``huge crowd gathered...to watch the encounter'' in the words of Dáithí Ó hÓgáin, so there was an immediate oral tradition surrounding the event, which often did not at all resemble what was recorded as having taken place. For example, Ó hÓgáin writes of one account casting d'Esterre as;

"...a professional gunman who lived in the West Indies. It was said he was the best shot in the world, and so the British offered him a huge amount of money if he would come to Ireland and challenge Daniel O'Connell to a duel."

In another account from Ríonach Uí Ógáin's Immortal Dan, Ó Conaill's victory is given a whiff of divine intervention, something that would have appealed to the sense of religious persecution of the Catholic underclass by the Protestant establishment:

''But when the order was given for to fire, D'Esterre's pistol locked and Dan blew his brains out. And the people said that is was just God's will.''

All of which is a very long way to go to illustrate that the folk memory of the event does not always clarify the particulars of a historical event (though it often does!), but it can inform one a great deal about the actual perception of the events by the people who experienced them.

Sources for the above excerpts and this material in general are Ríonach Uí Ógáin's Immortal Dan as mentioned, and Dáthí Ó hÓgáin's The Hero in Irish Folk History. I apologize if this is a somewhat incoherent response to your question, I'm rather getting used to writing in a comment field.

To add from the perspective of archaeology in the New World, "folk memory" in our case often takes the form of oral history. This isn't necessarily exactly the same as "folk memory" in the sense that oral history tends to be more formalized, both in the structure of what it says and how it is passed down. This isn't personal or anecdotal information, it is the way certain societies transmit their history in the same way that we tend to pass on our history in written form.

In that sense, as already mentioned, it really isn't all the different from written documents in the kind of concerns you would have in interpreting it. As mentioned, there isn't anything inherently more accurate of truthful about written documents. That said, that isn't a perspective all archaeologists share. Indeed, while archaeologists in the early 19th century tended to view indigenous oral history as a valuable source of data on past lives, it fell out of vogue mid-century. Only in the last 20-30 years has it really come back into the profession as a valued source of data by the majority of New World archaeologists, especially in the USA and Canada. This is especially true of historical archaeology in the US that tends to research the periods of European colonialism in the US (and Canada). Oral histories often have much more to say about this time period in particular because it is closer to the present when these oral histories are being told. That said, there are certainly deep time oral histories that have also proved useful (such as the aboriginal oral histories in Australia that have recently been correlated with geological events established through geologic lines of evidence).

In the US particularly archaeologists have really used oral histories of indigenous groups as a way to help interpret their archaeological discoveries. As a rule, archaeological evidence is really good at telling you what people did and how they interacted with other people, but much less useful for telling you what they thought about their behaviors or those people (beyond what their actions can tell us). This is where oral history has been most helpful.

That said, as already mentioned, you can't uncritically apply oral histories to developing a historical narrative, but they are certainly a very valuable kind of evidence to use in conjunction with archaeological and documentary evidence which have their own strengths and limitations. Using all three together helps create a richer picture of the past.