Early in David Hackett Fischer's Champlain's Dream, Fischer argues that Samuel de Champlain might have been the illegitimate son of the future Henri IV, king of France. Fischer acknowledges that he has no direct evidence to establish this as fact. He has no birth certificate with Henri's name on it. He has no document in which Henri acknowledges Champlain as son, or in which Champlain acknowledges Henri as father. No one from the time talks about such a father-son relationship between the two. Nonetheless, argues Fischer, if Champlain was indeed Henri IV's son, and if Henri was aware of that fact, then that would explain a host of peculiarities in Champlain's relationship to Henri IV and to the French state more generally. Moreover, he argues that it would explain these peculiarities in a way that no other hypothesis has heretofore been able to do.
There is no need here for us to get into the details about this argument, for it matters not for our purposes. What matters is that this stands as a wonderful exemplar of how one versed in Lonergan's epistemology would proceed. Fischer understands that what constitutes a historical hypothesis is not ultimately our observational apprehension of the data but rather our inferential apprehension of the relationships between the data. That is to say, history is not exegesis: it is not the interpretation of documents followed by pronouncements about whether their claims are true. As such, the fact that Fischer has no document explicitly identifying Henri as Champlain's father is no impediment to his hypothesis. At the same time, Fischer recognizes that the mere fact that by considering those relationships he can construct a hypothesis in which Henri is Champlain's father is not sufficient to establish that this is the case. Anyone can construct hypotheses. What separates the adults from the children is the ability to determine which hypotheses are most probable. Towards that end, Fischer advances a criterion by which to judge whether this is the best hypothesis on the matter, namely that of scope: does this hypothesis explain a greater scope of relevant data than does any competitor? He is cautious: acknowledging that in this case the data is such that he cannot say with certainty that Henri was Champlain's father, but nonetheless presenting it as a possibility that is perhaps to be preferred to its alternatives.