Law 101 for Experts: Understanding the Legal System

Expert witnesses are specialists in their own fields. Yet an expert witness may have never had an experience with the legal system before being asked to testify as an expert. 

Dani Alexis Ryskamp, J.D.

Written by
— Updated on April 26, 2022

Law 101 for Experts: Understanding the Legal System

A basic understanding of the civil trial process and the legal system will help an expert witness perform to the best of their ability. Knowing the role the attorney asked you to play can help you prepare reports and testimony, ask insightful questions, and collaborate more effectively with attorneys. 

In the United States, over 12 million non-traffic-related civil cases are filed in state courts each year. According to the Court Statistics Project. Approximately 286,289 civil cases were filed in U.S. federal courts in 2019.

Not all of these cases require the assistance of an expert witness. All cases, however, follow the same basic procedure:


First, the plaintiff files a complaint. The complaint must state a cause of action against at least one other party. The complaint is served on the named party or parties. The party or parties generally file an answer and/or one or more motions relevant to the complaint. One example is a motion to dismiss. Generally, the plaintiff is the party that files the complaint. The defendants are the parties who must respond.


Next, the case enters a phase known as discovery. During this phase, the parties exchange information and identify the actual issues in the case. At this phase, most states require the parties to disclose to one another the identities of any expert witnesses they plan to retain. This is the most common phase at which an expert witness first joins the case.

As the issues become clear during discovery, one or more parties may file a motion for summary judgment or for any number of other issues or purposes. The court may also issue scheduling orders, set a trial date, or take other steps to move the case along. The parties may also attend mediation, attempt to negotiate a settlement, or both.

Settlements, mediation, motions, and other means of resolving or disposing of a matter end many federal and state civil claims. If these methods fail to produce a resolution or disposition, however, the case may go to trial.


At trial, the expert witness’s role is twofold. The expert provides necessary specialized background information for the judge and jury to understand a material issue in the case. The expert may also provide an informed opinion. The second role differs from that of an ordinary witness. An ordinary witness sticks to only the facts of what they saw, heard, or did.

The Case From a Lawyer’s Perspective: What Retaining Lawyers Need to Prove

An attorney who retains an expert witness already has a basic understanding of the issues in the case. Typically, the attorney is thinking in terms of the cause of action and its elements.

The attorney can state any claim that a court can address in terms of a “cause of action.” Common causes of action an expert might encounter are negligence, wrongful death, products liability, and medical malpractice, although others exist.

Each cause of action can be broken down into its basic elements. For example, the elements of medical malpractice in most U.S. jurisdictions are:

  • The defendant (typically a medical provider) had a duty to provide care to the plaintiff that met the agreed-upon standard of care
  • The defendant breached that duty by falling short of the standard of care
  • The breach caused the harm of which the plaintiff complains
  • That harm is a type that can be addressed with money damages or other methods within the court’s power to impose

It’s important for expert witnesses to know the basic elements of the cause of action because an attorney may not ask the expert to address every element.

For instance, in some states (such as Indiana),  a panel of similarly-situated medical experts decides whether a defendant breached the standard of care. An attorney will not ask an expert witness to opine on whether the breach occurred. However, an expert may be asked to explore issues of causation or damages. An expert who is aware of the elements can focus on the relevant ones.

A complaint in any civil case may state more than one cause of action. When causes of action overlap (as with medical malpractice and wrongful death, for example), it’s important the expert understands where the elements overlap and how they will affect the expert’s focus.

Common Defenses Against Common Causes of Action

In addition to considering the elements of each cause of action stated in the complaint, an attorney seeking an expert witness will also consider common defenses to a cause of action.

Commonly-raised defenses include:

  • The statute of limitations has expired—i.e. the case was filed too late.
  • The plaintiff is partly or wholly responsible for their own harm under a theory of comparative or contributory negligence
  • The plaintiff agreed to the risk of harm, known as “assumption of risk”

At times, these defenses overlap with the work the attorney asks the expert to do. For example, imagine a statute of limitations for medical malpractice requires a case to be filed “within two years of the date the plaintiff knew or could reasonably have known about the harm.” If the timing of the plaintiff’s knowledge is in dispute, the expert witness might be asked to opine about the earliest date at which the plaintiff “could reasonably have known” about their condition—especially if there are disputing claims about whether this date lies before or after the two-year cutoff.

Expert witnesses are not required to be experts in civil claims. Having a basic understanding of the key elements of claims and defenses and the legal system, however, can help an expert witness ask the right questions and provide the most effective assistance.

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  1. well delineated, very helpful in understanding roles and responsibilities.

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