Rules of evidence are the trial system’s equivalent of the rules of grammar. Just as grammar rules govern how we speak and write, evidence rules control courtroom procedures. Evidence rules limit not only what witnesses and lawyers can say during trials, but also how they can say it.
Evidence rules guide the process by which information (evidence) flows from witnesses to a judge or jury. The rules control both the content of evidence and the manner in which it’s presented. To take a familiar rule, witnesses may testify only in response to questions, rather than by telling a long, uninterrupted narrative. Another widely known rule deals with hearsay—it bars witnesses from testifying about certain statements made outside the courtroom.
Most evidence rules developed through “common law” judicial decisions. Today, most evidence rules are found in statutes. California was one of the first states to enact a comprehensive set of evidence laws, known as the California Evidence Code. The California code was a primary model for the Federal Rules of Evidence (“FRE”), a set of laws that governs trials in federal courts. About 40 states have enacted evidence rules based on the FRE. Because every jurisdiction’s evidence rules are based on the common law and on each other, evidence rules are largely similar throughout the country.
For the most part, judges no longer make evidence rules. With some exceptions, legislatures have taken over the development of evidence law. Lawmakers know that evidence rules are vital in determining the outcomes of cases, and they want to have primary influence in shaping those rules. Of course, it’s up to judges to interpret the evidence rules that legislators produce, and, in doing so, they can substantially alter the scope and meaning of those rules.
Many evidence rules consist of general guidelines, leaving judges to interpret them according to the circumstances of each case. For example, assume that an evidence rule provides that certain kinds of documents have to be shown to have been prepared in a trustworthy manner before a judge can admit them into evidence. What’s trustworthy to one judge might not be to another, and will depend on the circumstances of preparation. For example, a judge is likely to hold a sophisticated police laboratory to a different standard than a mom-and-pop grocery store when it comes to documenting transactions.
In most jurisdictions, the evidence rules in criminal cases are largely the same as those in civil cases. The FRE, for example, apply to both civil and criminal trials. However, certain evidence rules apply differently depending on the kind of case involved. An example is FRE 404(a), which allows criminal defendants to introduce evidence about their or their alleged victims’ character in many cases. (Character evidence is otherwise generally inadmissible.)
If you’re facing criminal charges, you’re almost always best off letting a lawyer represent you. The rules of evidence are tremendously complex and nuanced; only an experienced attorney will be familiar enough with them to provide a competent defense to criminal charges.