How much doubt is reasonable? 

As a student of the English language, I'm convinced that doubt isn't a reasonable thing in any of its many forms.
 
What I mean is that doubt is nothing but a feeling. A person can doubt the existence of God or doubt that she's going to forget her phone number in the next two hours. A person can doubt another person's statements because of a gut feeling based on her understanding of neuro-linguistics (eye movements) or body language. That's what jurors are asked to do all the time--look at testimony skeptically.

In my opinion, the jury instruction that the prosecution must prove its case "beyond a reasonable doubt" is silly. And I know this is a phrase that is now prescribed in all criminal trials by the U.S. Supreme Court. I've researched the history of this phrase extensively, and what I've learned can't be boiled down to a blog post. (Maybe I'll write an article on the topic one of these days.)

But I think that what my gorgeous librarian-sleuth, Iris Ginge, concludes in The Juror Investigates is what judges really ought to tell juries: "The prosecution is presumed to be mistaken unless and until it proves otherwise."