This study explored how historians with different background knowledge read a series of primary source documents. Two university-based historians thought aloud as they read documents about Abraham Lincoln and the question of slavery, with the broad goal of understanding Lincoln's views on race. The first historian brought detailed content knowledge to the documents; the second historian was familiar with some of the themes in the documents but quickly became confused in the details. After much cognitive flailing, the second historian was (...) able to piece together an interpretative structure that brought him by the task's end to where his more knowledgeable colleague began. Data analysis focused on how, lacking detailed content knowledge, this historian was able to regain his intellectual footing, work through confusion, and resist the urge to simplify. Implications of this work for cognitive analyses in history and education are discussed. (shrink)