This segment begins with a student raising doubts about the reliability of one of the sources in the document set that was written by a historian. Another student builds on his argument by noting that the source “doesn’t show where he got his information from.” In responding to these skeptics, the teacher engages in a few moves that push the discussion forward. First, she elicits a counter-argument (namely, that the author has “street cred” because he’s a professor at a university). Second, she polls students as to whether they find the source reliable, indicating by doing so that students can take either perspective at this point in the discussion. Finally, she returns to the discussion at hand: “if you think this document is pretty reliable, how is Islam spreading? According to this document?” By returning to the central question, the teacher demonstrates a key take-away of historical discussions: the evaluation of trustworthiness must occur in the service of historical understanding. The students who question the reliability of this particular source might still agree with the author’s argument if it appears in other sources that they find more credible.