The practice of picking a thesis and then setting out to establish it is a widespread intellectual pursuit. But biographers and historians sometimes portray their subjects as if the historical participants could recognize what lay ahead of them.
Assuming that people of the past pondered over the events of their day from the same perspective as we do in the present is committing The Historian’s Fallacy.
The notion of the historian’s fallacy was first presented by the British literary critic Matthew Arnold (1822–88) in his The Study of Poetry (1880.) In questioning how historical backgrounds were portrayed in the development of literary styles, Arnold called attention to the frequent logical error of using hindsight to assign a sense of causality and foresight of significant historical events to the people who lived through them. In reality, those historical participants may not have had wide-ranging perspective that we assume in interpreting the context, conventions and limitations of their time. Arnold wrote,
The course of development of a nation’s language, thought, and poetry, is profoundly interesting; and by regarding a poet’s work as a stage in this course of development we may easily bring ourselves to make it of more importance as poetry than in itself it really is, we may come to use a language of quite exaggerated praise in criticising it; in short, to overrate it. So arises in our poetic judgments the fallacy caused by the estimate which we may call historic. … Our personal affinities, likings and circumstances, have great power to sway our estimate of this or that poet’s work, and to make us attach more importance to it as poetry than in itself it really possesses, because to us it is, or has been, of high importance.
The American historian David Hackett Fischer, who coined the phrase “historian’s fallacy,” cited the claim that the United States should have anticipated Japan’s surprise attack on Pearl Harbor because of the many warning signs that an attack was in the cards. Fischer argues those signs seem obvious only in hindsight—to the World War II military leaders, many of those signs suggested possible attacks on many positions other than Pearl Harbor.
A good historian strives for objectivity by ignoring his own knowledge of consequent events and employing only what the historic individuals would have known in the context of their own time.
A related fallacy is Presentism—a manner of historical analysis wherein the past is interpreted by means of present-day attitudes. Presentism often fosters moral self-righteousness. Employing present-day moral standards to reflect on the Founding Fathers’ ownership of slaves, David Hume’s racism, or Gandhi’s opposition to modernity and technology should not be tainted by our stance of temporal condescension.