At every point in his task, the historian is faced with two essential and frequently-conflicting duties: the responsibility to tell us what really happened, and the responsibility to tell us the significance of what happened. Without the latter, all he provides is a disjointed chronicle, a sequence of happenings with no clear logic to them, which is not history. But as soon as he attempts to tell us the significance of what happened, he risks undermining his first responsibility. For to make sense of what happened, he must place it in a narrative, make it part of an unfolding process with an inner logic and coherence, a causal sequence that has a certain air of inevitability. But of course, that is not how events actually happen. The narrative into which the event is later placed does not yet exist when it takes place; the subsequent events are all as yet contingent, not inevitable. To describe an event, then, in light of the events that succeeded it is to be, in a certain sense, false to it, since none of those who experienced it (unless they are remarkably prescient) experienced it in that light.
Peter Leithart provides a compelling illustration of this problem in Deep Exegesis, discussing the example of the Defenestration of Prague—when the Bohemians threw two imperial ambassadors out the window of Prague Castle (they were lucky enough to land safely in a pile of manure), setting in motion a chain of events that caused the Thirty Years' War. It is customary, therefore, for historians to describe the Defenestration as the event that started the Thirty Years' War. And yet while clearly true in one sense, at the time, this was far from true. It was not clear at the time that anything more than a diplomatic insult had occurred; a war was far from inevitable, much less one lasting thirty years. In this case the falsehood is perhaps minor and forgivable, and in any case the task of history cannot do without such narratives, but in other cases this hindsight viewpoint perpetrates much more serious misconstruals of events, portraying radically contingent events as an inevitably unfolding sequence, obscuring the fact that the final outcome long hung in the balance.
Perhaps it is merely because I spend more time in the field, but it is my suspicion that Reformation historians are particularly prone to this kind of hindsight bias. It is not hard to see why. What was at the time a chaotic and inchoate reform movement or cluster of reform movements, led by dozens of men from different backgrounds, of different abilities, and possessed of different visions, eventually brought forth a set of fairly well-defined denominational traditions: Lutheran, Anglican, Reformed, Baptist—each of these capable of further subdivision, especially the Reformed. Seeking to bring order out of the chaos of the sixteenth-century, nothing is easier than for historians to take these later divisions as their starting point, and proceed to narrate the Reformation as the seemingly-inevitable unfolding of nascent disagreements into these permanently-divided traditions. Indeed, a sort of contest ensues, whereby historians try to outdo one another in finding the earliest seed of these subsequent divisions: the development of the Reformed can be traced by to 1550—no, 1540—no, 1530—no, 1520.
One cannot deny, of course, that these efforts are often fascinating and instructive, helping to make sense of later developments that otherwise would seem random and illogical, without precedent. We cannot do without these attempts to draw out the enduring significance of 16th-century events. But we must be careful not to let them cloud too much our understanding of what really happened, or to flatten out complex spectrums of disagreement into two rival incompatible positions. Reformation historiography, in many ways, is still just beginning to come to terms with the extent of its hindsight bias. The myth of Anglicanism as an independent movement, discernible as such from the beginning, is dying very hard indeed. The sharp and straightforward divide between "Erastianism" and Calvinist ecclesiology, between Zurich and Geneva, is another favorite narrative schema, which despite being rendered increasingly untenable by fresh scholarship, continues to hold sway in most Reformation histories.
Perhaps the most pervasive such hindsight dichotomy, which continues to bedevil Reformation scholarship, seriously impairing understanding of how the key actors at the time actually perceived themselves and their work, is the Lutheran-Reformed divide. Of course, clearly enough, the two traditions had diverged quite decisively and irremediably by the end of the 16th century, and went on to develop independent bodies of theology, liturgy, hymnody, etc. Moreover, clearly enough, the disputes between them can be traced well back into the early Reformation period, and were fought out sharply by some participants. Few sensible historians could deny, I think, that after the death of Melanchthon in 1560, the two branches had diverged fundamentally and, barring a radical reversal, irreconcilably—though even this was probably not clear to many observers at the time. But few historians are content with this claim.
On the contrary, nothing is more common in Reformation histories than to find a line like this: "Once it became clear that Luther and Zwingli would not come to agreement on the interpretation of the Lord's Supper, a split became inevitable between the Lutherans (or, to use the terminology of the day, the "evangelicals") and the Reformed" (Glenn Sunshine, "Discipline as the Third Mark of the Church: Three Views"). The Colloquy of Marburg, 1529, is identified as this decisive point of disagreement, the watershed from which, inevitably, flowed forth two distinct streams of the Reformation. (Needless to say, once this watershed has been anchored in the minds of historians, they cannot rest content with it, but proceed backward to the beginning of Zwingli's teaching in the early 1520s as the point of departure.) And of course, if the two streams are already fundamentally distinct after 1529, then historians have no hesitation in discussing "Lutheran" and "Reformed" theologians as clearly separate groups in the 1530s, 1540s, and so on, despite the ambiguities and anachronisms thus produced, and in explaining events in terms of the deep-seated and irreconcilable conflict between these two (so that theologians are forever being described as "doing X in order to distance themselves from the Reformed" or "doing Y in order to conciliate the Lutherans" and so on).
It almost goes without saying, however, that if we are describing the events of the 1530s and 1540s from the point of view of the self-understanding of those involved, this dichotomy rarely holds. Most Protestants, at this time, viewed themselves as part of a single group, within which there existed significant differences of opinion on certain points, along what was a fairly continuous spectrum, rather than a simple dichotomy. Of course, historians have increasingly recognized the common ground between Calvin and Melanchthon, for instance, but what is true remarkable is that not even Marburg was the great Parting of the Ways that it has been routinely identified as in subsequent narratives. On the contrary, the theologians who gathered at Marburg were conscious of significant potential disagreements beforehand, and recognized the importance of coming to some kind of unity, to ensure the success of the Reformation. And believe it or not, they succeeded in large part. at the conclusion of the meeting, they drew up 15 Marburg Articles, covering the different topics they had debated. On fourteen of the articles, they professed themselves in full agreement; the Eucharist was the only one where differences remained, and even here, they were able to delineate significant areas of common ground. Melanchthon considered the meeting a good success, and many theologians over the following years had great confidence that the remaining disagreement would be readily resolved.
And indeed, so it might have seemed to be by the 1540s as key leaders Calvin and Melanchthon reached a meeting of the minds—only for renewed conflict in the 1550s to drive a deep wedge between the parties. In hindsight, of course, we can see that not only on the Eucharistic issue, but on other matters as well, "Lutheran" and "Reformed" theologians were starting to highlight different themes which would give in the end a fundamentally different character to the two traditions. We would be foolish to do without the benefit of this hindsight; but we are foolish also when we allow it to blind us to a clear vision of events as they actually occurred.