Barry’s use of the sententia informs the readers of the necessity of “doubt.” Doubt by itself is not sufficient enough to make a scientist great; as Barry states, a scientist must undergo investigations in order to confirm or deny their doubts through any means possible. The readers must know that perseverance is mandatory, even when given nothing but their hands to uncover the truth. The inclusion of the quote from a renowned scientist further strengthens the credibility of the advice. Barry also uses the quote from Claude Bernard as a metabasis for moving onto talking about a scientist’s ability to doubt himself. This gives the readers a new train of thought to follow, but without disrupting the