Witness testimony provides the first draft of history and requires a kind of reading that connects descriptions of events from many perspectives and sources. This chapter examines one critical step in that connective process, namely, how to assess a speaker's certainty about the events they describe. By surveying a group of approximately 300 readers and their approximately 28,000 decisions about speaker certainty, this chapter explores how readers may think about factual and counterfactual statements, and how they interpret the certainty with which a witness makes their statements. Ultimately, this chapter argues that readers of collections of witness testimony were more likely to agree about event descriptions when those providing the description were certain, and that readers' abilities to accept gradations of certainty were better when a witness described factual, rather than counterfactual or negated events. These findings lead to a suggestion for how researchers in natural language processing could better model the question of speaker certainty, at least when dealing with the kind of narrative nonfiction one finds in witness testimony.