What aspect of a text allows a reader to decide if an argument is sound or valid?

The aspect of a text that enables a reader to determine if an argument is sound or valid is credibility. Credibility refers to the trustworthiness and reliability of the sources used in forming the argument, as well as the author's qualifications and background. An argument grounded in credible evidence and presented by a knowledgeable author enhances its validity, allowing readers to assess whether the claims made are well-supported and logically coherent.

When evaluating an argument, a reader considers the credibility of the evidence provided—whether the facts, statistics, and references are derived from reputable sources that are known for accuracy and expertise in the subject matter. This context is essential in establishing the strength of an argument, helping the reader to form a judgment about its soundness.

Other options like text evidence, contrast, and summation each play different roles in understanding a text but do not directly influence the determination of an argument's validity in the same way that credibility does. For example, while text evidence is crucial for supporting an argument, it is the credibility of that evidence that ultimately impacts the reader's judgment on the argument's soundness.