Reagan v. United States was a Supreme Court case in 1894 that revolved around the issue of jury instructions and whether or not they were prejudicial to the defendant, John Reagan. The court ruled that while it is important for judges to provide clear instructions to juries about how they should consider evidence, these instructions must be fair and unbiased towards either party involved in the trial. In this particular case, Reagan had been convicted of murder based on circumstantial evidence alone. His defense argued that the judge's instruction regarding reasonable doubt was biased against him because it suggested that jurors could convict even if there was some doubt about his guilt as long as their doubts weren't "reasonable". The Supreme Court agreed with this argument and overturned Reagan's conviction due to unfair jury instruction.

In the dissenting opinion for Reagan v. United States, Justice Brewer argued that the jury was not properly instructed on how to consider evidence of good character in relation to reasonable doubt. He believed that a defendant's previous good character should be considered as an independent factor in determining guilt or innocence, rather than merely being used to tip the scales when other evidence creates uncertainty. In his view, this misinterpretation could have potentially influenced the jury's decision and thus he disagreed with affirming conviction based on these grounds.