Atticus believes that an accused man deserves more than just the expectation of "reasonable doubt" when it comes to being found innocent or guilty. According to Atticus,
"... in the absence of eye-witnesses there's always a doubt, sometimes only the shadow of a doubt. The law says 'reasonable doubt,' but I think a defendant's entitled to the shadow of a doubt." (Chapter 23)
Atticus believes, as many people do, that the slightest possiblility of innocence, no matter how "improbable," should prevent a defendant from being adjudicated guilty or jailed. As Jem points out, such decisions can only be left up to a jury, and Atticus believes that
"We generally get the juries we deserve." (Chapter 23)
Atticus also believes that charges stemming in capital punishment should require at least one or two eye-witnesses before the death penalty is handed down.
"Someone should be able to say, 'Yes, I was there and saw him pull the trigger..." (Chapter 23)
In chapter 23, Atticus and Jem are discussing the verdict of Tom Robinson and the laws surrounding rape. Tom Robinson should never have been tried for the crime he was charged with because there was no evidence to prove that he raped Mayella Ewell. However, back in the South in the 1930s, all it took for a black man to go to court were the accusations of a white man. Many other aspects of the law were ignored when Tom Robinson was arrested and tried, but basics, such as evidence, jury by one's peers, and reasonable doubt never even entered the debate! Most importantly, there was an absence of eye-witnesses in the case between the Ewells and Tom Robinson, about which Atticus says the following:
"In the absence of eye-witnesses there's always a doubt, sometimes only a shadow of a doubt. The law says 'reasonable doubt,' but I think a defendant's entitled to the shadow of a doubt. There's always the possibility, no matter how improbable, that he's innocent" (219-220).
Eye-witnesses, or physical and inarguable evidence, are key to whether there is "reasonable doubt." Today, if there is any doubt whatsoever that a person committed a crime, it is difficult to get a conviction. Atticus would have liked that belief back in 1935 because he believed, as all should have, that without proof or eye-witnesses, no one should be tried or even sent to jail for a crime. In a way, Atticus believes that everyone should be given the benefit of the doubt and freed rather than being convicted on circumstantial evidence or the defensive claims of people like the Ewells. Unfortunately, because of racism and acute prejudice, African Americans fell victim to hearsay as the only evidence to convict them at the time. Therefore, Atticus believes that if there is any doubt, no matter how small or insignificant, that person should be freed and not convicted.
When Atticus agrees to defend Tom Robinson, he knows that in all reality, there is no way Tom will be found innocent. He knows that in a town like Maycomb, a black man is not going to get a fair trial, but he believes that no matter the color of a person, they deserve at least a shadow of a doubt to prove their innocence. Atticus knows that even a shadow of doubt will most likely not save Tom.
"In the absence of eye-witnesses there's always a doubt, sometimes only a shadow of a doubt. The law says 'reasonable doubt,' but I think a defendant's entitled to the shadow of a doubt."
Atticus proves there is reasonable doubt when he shows the court that Tom can't move his left arm. This shows that Tom was not capable of committing the crime and should have placed doubt in the minds of the jury. Because Tom was a black man, the jury had already made up their mind before the trial even began. Atticus still believed in the law and proved reasonable doubt, although in the end it didn't matter.
It just goes to show us what kind of man Atticus really was. He fought for what was right and fair. He believed in justice, yet he knew the ugliness that came with the prejudice in the county. He taught Jem and Scout the truth about people and expected them to always do what was right. Just as he did. Harper Lee created a character that after all these years still means so much to us and is a character we call all learn from.