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Defining Evidence

G. Alexander Nunn, Defining Evidence in Nunn on Evidence (2025), available at https://nunn.law/defining-evidence. | View history

Before we embark on a journey through the intricate rules and doctrines that govern what a jury may hear or a judge may consider, we must first establish a clear understanding of our subject's very essence. What, precisely, is evidence within the context of our legal system? This initial exploration is not merely an academic exercise; it is the bedrock upon which all subsequent understanding of trial practice, factual determination, and ultimately, the pursuit of justice is built. Consider this chapter the crucial first step in appreciating how our adversarial system attempts to unearth truth from the often-murky depths of human conflict and recollection. We will begin by defining this core concept, exploring its fundamental purpose, and drawing a critical distinction between the information presented and the conclusions that may be drawn from it.

Key Overview

At its heart, the concept of evidence is deceptively simple, yet profoundly significant. It forms the informational currency of our legal system, the raw material from which factual narratives are constructed and upon which legal judgments depend. Without evidence, the resolution of disputes would be reduced to a matter of speculation, bias, or sheer power, rather than a reasoned process of inquiry. Therefore, grasping its nature and its primary role in legal proof and factfinding is paramount for any student of the law.

The term 'evidence,' in its broadest legal sense, refers to any species of information that is presented to a court or other adjudicative body with the objective of proving the existence or non-existence of a fact that is in dispute between the parties. This information can manifest in a multitude of forms. Perhaps the most commonly envisaged form is testimonial evidence, which consists of the sworn statements of witnesses who recount their observations, experiences, or knowledge relevant to the case. This might be an eyewitness describing an accident, a victim identifying an assailant, or an expert witness offering a professional opinion. Another crucial category is documentary evidence, which encompasses a wide array of writings and recordings. This could include contracts, letters, emails, business records, official government documents, or even digital communications. Beyond testimony and documents, we have real evidence, sometimes referred to as physical evidence. These are tangible objects that can be directly examined by the factfinder, such as a weapon allegedly used in an assault, a defective product in a liability case, or a photograph depicting a relevant scene. More modern conceptualizations also comfortably include demonstrative evidence, which is not itself a direct piece of the factual puzzle but rather aids in understanding other evidence, like charts, diagrams, or animations. Finally, information can also be presented through sensory perceptions allowed by the court, or data derived from scientific processes, such as DNA testing. The critical commonality across these diverse forms is their role as information bearers, offered to shed light on the contested factual questions that a legal proceeding aims to resolve.

The core purpose of introducing evidence into a legal proceeding is to facilitate the process of legal proof and thereby enable effective factfinding. In any contested case, whether civil or criminal, the parties advance competing versions of events or differing assertions about critical facts. The adjudicative process, whether presided over by a judge alone or a judge and jury, is fundamentally an effort to determine which version of the facts is more likely true, according to the applicable legal standards. Evidence is the indispensable tool for this undertaking. It provides the factual basis upon which judges and juries can reconstruct past events, understand present circumstances, and ultimately, make informed decisions about the rights and liabilities of the parties involved. The ultimate aim is to arrive at a determination of truth concerning the specific, material facts that are in dispute. Through the structured presentation and careful consideration of evidence, the legal system strives to ensure that outcomes are based on a rational assessment of information, rather than on unfounded assumptions or conjecture. It is through this mechanism that the abstract principles of law are applied to concrete factual realities.

Distinguishing Evidence from Proof: A Crucial Clarification

Having established what evidence is—information presented to resolve factual disputes—it is absolutely essential to distinguish it from a related, yet distinct, concept: proof. While laypersons often use these terms interchangeably, in the precise language of the law, they carry different meanings. Evidence, as we have discussed, comprises the various forms of information—the testimony, the documents, the physical objects—that are proffered to a court. Think of it as the collection of clues, data points, or informational items laid before the factfinder.

Proof, on the other hand, is the result or the effect of considering that evidence. It is the cognitive outcome achieved when the evidence presented is deemed sufficient to convince the factfinder of the truth of a particular factual proposition to the requisite degree of certainty. In simpler terms, evidence is the means, and proof is the end. A single piece of evidence, standing alone, rarely constitutes proof of a disputed fact. For instance, a witness testifying they saw the defendant near the scene of a crime is evidence. However, that testimony alone might not be sufficient to constitute proof that the defendant committed the crime, especially if other evidence contradicts it or offers an innocent explanation. Proof arises when the totality of the evidence presented and considered persuades the mind of the trier of fact that a certain fact is true, according to the standard of proof applicable in that particular type of case (such as "beyond a reasonable doubt" in criminal cases or "preponderance of the evidence" in most civil cases). Thus, evidence is the raw material, the informational input, while proof is the intellectual conviction, the persuasive output, derived from the evaluation of that material. Understanding this distinction is vital because the legal system is not only concerned with what information is presented but also with whether that information, cumulatively, meets the necessary threshold to establish a fact as proven.

The Framework of Admissibility: Governing Rules of Evidence

While evidence encompasses a broad array of information offered to prove or disprove a fact, it is not the case that any and all information a party wishes to present will automatically be considered by the factfinder. The legal system has developed a comprehensive set of principles and regulations, known as the rules of evidence, to govern the admissibility of information in legal proceedings. The primary purpose of these rules is to ensure that the evidence upon which legal decisions are based is reliable, relevant, and fair, and that the trial process itself is efficient and just.

In the federal courts of the United States, the paramount source of these regulations is the Federal Rules of Evidence (FRE). Most state jurisdictions have adopted their own evidence codes, many of which are closely modeled on the FRE, though variations certainly exist. These rules act as a sophisticated filtering mechanism, dictating what types of information may be presented to the judge or jury, under what circumstances, and in what manner. They address a vast array of issues, such as the competency of witnesses, the requirements for authenticating documents and objects, the use of expert testimony, and the exclusion of evidence deemed unfairly prejudicial, misleading, or based on unreliable hearsay.

It is crucial to understand at this introductory stage that our current discussion is strictly focused on the conceptual definition of evidence. We are exploring what evidence is, not the detailed mechanics of how it is admitted or excluded. Therefore, any specific discussion of individual rule numbers, such as FRE 401 concerning relevance or FRE 403 regarding the balancing of probative value against prejudicial effect, is deliberately deferred to subsequent chapters. Similarly, the intricate standards governing the admissibility of various types of evidence will be explored in dedicated sections later in this treatise. For now, it suffices to recognize that a structured framework of rules exists to ensure the integrity of the factfinding process by controlling the flow of information to the trier of fact. These rules aim to enhance the truth-seeking function of trials while safeguarding fundamental fairness.

Evidence and the Burden of Proof: An Introductory Nexus

The concept of evidence is inextricably intertwined with another fundamental legal principle: the burden of proof. In any legal proceeding, whether civil or criminal, the adversarial system assigns responsibilities to the parties involved. One of the most critical of these responsibilities concerns the necessity of producing evidence and persuading the factfinder. The burden of proof dictates which party has the obligation to come forward with evidence to support its claims and, ultimately, which party bears the risk of not persuading the trier of fact.

At a high conceptual level, the party asserting a particular fact or claim generally bears the initial burden of producing some evidence to support that assertion. If a party with this initial burden fails to offer any credible evidence on a necessary element of their case, their claim may fail as a matter of law before even reaching the stage of full factual deliberation. Beyond this initial obligation to produce evidence, there is also the burden of persuasion – the ultimate task of convincing the factfinder (judge or jury) that their version of the facts is true to the extent required by the applicable legal standard (e.g., preponderance of the evidence, clear and convincing evidence, or beyond a reasonable doubt). The quantum and quality of evidence presented by each side are what the factfinder will weigh in determining whether a party has successfully met its burden of persuasion.

This treatise will delve into the nuanced distinctions within the burden of proof, such as the burden of production (the duty to introduce enough evidence on an issue to have that issue decided by the factfinder rather than ruled upon as a matter of law by the judge) and the burden of persuasion (the more substantial obligation to convince the factfinder of the truth of a proposition) in much greater detail in Chapter 11. Our purpose here is merely to highlight the conceptual linkage: evidence is the very substance that parties use to attempt to satisfy their respective burdens of proof. The rules of evidence will determine what information is admissible for this purpose, but the concept of the burden of proof dictates who must produce it and who bears the risk if the factfinder remains unpersuaded.

The Confines of Our Present Inquiry

It is important to reiterate the specific and intentionally limited scope of this introductory section. Our focus here has been squarely on addressing the fundamental question: "What is evidence?" We have defined it as information used to prove or disprove facts in dispute, explored its core purpose in legal proof and factfinding, and clarified the crucial distinction between evidence as information and proof as the cognitive result of evaluating that information. We have also briefly acknowledged the existence of governing rules, like the Federal Rules of Evidence, that frame its admissibility, and noted its conceptual relationship with the burden of proof.

However, this exploration has deliberately refrained from delving into the complex and fascinating questions of how evidence is evaluated, how much weight it should be given, or the specific legal standards and procedures governing its admissibility. Issues such as the principles of relevance (which will be a cornerstone of Chapter 2, examining concepts akin to those in FRE 401), the balancing of probative value against the danger of unfair prejudice (a topic for later discussion, akin to FRE 403), and the myriad specific rules governing hearsay, character evidence, expert testimony, and privileges are all reserved for detailed examination in subsequent chapters. Similarly, the procedural mechanics of authenticating evidence (the subject of Chapter 9) and the intricate dynamics of the burdens of production and persuasion (to be fully analyzed in Chapter 11) fall outside our current purview. Our sole objective in this section has been to establish a clear and robust conceptual understanding of evidence itself, laying a solid foundation for the more detailed explorations that will follow.

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