My historical review of the idea of history has resulted in the emergence of an answer to this question: namely, that the historian must re-enact the past in his own mind. What we must now do is to look more closely at this idea, and see what it means in itself and what further consequences it implies.
In a general way, the meaning of the conception is easily understood. When a man thinks historically, he has before him certain documents or relics of the past. His business is to discover what the past was which has left these relics behind it, For example, the relics are certain written words; and in that case he has to discover what the person who wrote those words meant by them.
This often seems to be misunderstood as meaning that re-enactment is a method; but I don't think this is Collingwood's point. Rather, the point is that this is the standard of success. A historian has succeeded in (say) understanding Plato's arguments to the extent that he or she can trace something like Plato's own steps with something like Plato's own reasoning, and the closer that "something like" is to "exactly like" the more successful the historian is. There should be a common structure between Plato's reasoning and the historian's reasoning; the historian of ancient philosophy is trying to synch his or her mind with Plato's, to the extent that's possible.
This gets more complicated when the relics aren't written words but something else (stone obelisks, or buttons, for instance), but reading Collingwood, it seems to me that he intends to include these as well. It's hard to say; he talks very abstractly at times, but most of his examples are written texts. This could just be because they are the most information-rich "relics of the past" that historians deal with. Re-enactment of the life of a button in one's mind has obstacles that arise from a lack of information. But certainly historians who deal with material culture could be said in some sense to try to re-enact the life of the button in their minds, and they know their trade the more they can use subtle clues to get something very like the actual life of the button. On the other hand, Collingwood repeatedly talks about it as if it's a problem of other minds, and we aren't dealing with other minds in the case of the button, unless, perhaps, we are thinking about trying to re-enact the mind of the button-maker as he carved this button, or something like that.
So the big question becomes: is there a fundamental difference between these two? Is re-enacting the thought of Plato fundamentally different from re-enacting the history of the obelisk or the button, because one involves a mind? Or do they involve the same kind of thinking, just applied to different evidence?