§ 1.03 Law of Evidence

• Jurisdiction: United States

§ 1.03 Law of Evidence

When first approached, evidence law can appear to be just a "bunch of rules"—and it is that. But there are several ways to classify the rules of evidence that may be of assistance.²¹ One way is by type of proof—testimonial, documentary, real, and so forth, as discussed in the preceding section. Another way is to divide the subject into major categories: (1) rules governing the substantive content of evidence, (2) rules governing witnesses, and (3) substitutes for evidence.

[A] Rules Governing the Content of Evidence

There are two main categories of evidentiary rules concerning the substantive content of evidence: relevance rules and competence rules.

[1] Relevance Rules

All evidence must be relevant. Irrelevant evidence is always inadmissible.²² Stated another way—relevancy is the threshold issue in deciding the admissibility of all evidence.²³ Because there are an almost infinite variety of relevancy problems, courts are given authority to make ad hoc judgments about the probative value of evidence.²⁴ Some situations have come before the courts so often that "rules of thumb" on admissibility have developed—e.g., "similar happenings," "adverse inferences," and "out-of-court experiments."²⁵ In other situations, categorical rules have developed. For instance, character evidence is generally prohibited, although there are exceptions.²⁶ Other relevance rules govern habit²⁷ and insurance evidence.²⁸

[2] Competence Rules

Relevancy, however, is not enough. Relevant evidence may be excluded for various reasons. These reasons are found in competence rules, which can be divided into two subcategories.

[a] Rules Based on Reliability Concerns

Sometimes courts exclude evidence because its reliability is suspect. The hearsay rule is an example. If an eyewitness from a bank robbery tells another person about the robbery, should that other person be allowed to testify about the robbery? The hearsay rule says "no." Defense counsel needs the opportunity to cross-examine the eyewitness about what that person saw. For present purposes, hearsay may be defined as an out-of-court statement offered for the truth of its assertion. There are, of course, numerous exceptions.²⁹ Another example is the "best evidence" rule. It comes into play when a party tries to prove the contents of a writing, which might be important in a contract dispute or will contest.³⁰ In short, sometimes the original must be produced.

[b] Rules Based on External Policies

Competency rules may also be based on some policy extrinsic to the trial process—i.e., rules of privilege. Communications between client and lawyer are excluded at trial in order to encourage such communications. Other common privileges include communications between husbands and wives, doctors and patients, psychotherapists and patients, and clergy and communicants.³¹ Those rules exclude evidence that may be both relevant and reliable.

[B] Rules Governing Witnesses

Rules relating to witnesses can be divided into several subcategories: (1) competency of witnesses, (2) examination of witnesses, (3) types of witnesses (lay and expert), and (4) credibility of witnesses. These were briefly touched upon in the previous section.

[1] Competency of Witnesses

The competency of a witness (as opposed to the competence of the evidence discussed above) refers both to the mental capacity of the witness to observe, recall, and relate what she has seen and to the moral capacity of the witness to recognize the obligation to testify truthfully. At common law, competency rules excluded any person with an interest in the case (including the parties), children, the insane, and so forth. For the most part, these rules have been transformed into credibility rules. Indeed, Federal Rule 601 states that everyone is competent to testify. Yet some problems remain,³² such as whether or not a two-year-old child should be permitted to testify.

[2] Examination of Witnesses

As noted in the previous section, there are housekeeping rules governing the order of evidence presentation at trial and the order of witness examination (direct, cross, redirect, and recross).³³ Additional rules...