CACI No. 400 and 401: the elements of negligence and the reasonable-care standard

CACI No. 400 is the opening instruction on the elements in a California negligence trial. It names three things the plaintiff has to prove. CACI No. 401 follows it and explains the standard the jury uses to decide the first of those three: whether the defendant was negligent at all. Read together, they set out the whole claim in fewer than two hundred words (CACI Nos. 400 and 401).

The three elements in CACI No. 400

Under CACI No. 400, the plaintiff wins only by proving all of these:

1. The defendant was negligent.
2. The plaintiff was harmed.
3. The defendant's negligence was a substantial factor in causing the plaintiff's harm.

The instruction uses the word harm throughout in place of loss, injury or damage. The Directions for Use explain that harm is broad enough to stand in for all of those terms. They also say that in a medical malpractice or professional negligence case, the word medical or professional goes in front of negligence in the opening paragraph.

The third element, causation, has its own instruction. CACI No. 430 defines a substantial factor, and our CACI No. 430 explainer covers how jurors apply it.

Where duty went

Law students learn negligence as four parts: duty, breach, causation and damages. CACI No. 400 lists only three, and duty is the one missing. The reason is who decides it. The Sources and Authority for the instruction cite California Supreme Court decisions leaving the existence of a duty to the judge as a legal question. The jury never sees it as an element because the judge has already resolved it.

The starting rule comes from Civil Code section 1714(a), which makes people responsible for harm caused by their failure to use ordinary care (Civ. Code § 1714). Courts carve out exceptions to that general duty only when public policy clearly supports one. The case law collected with CACI No. 400 traces this to Rowland v. Christian (1968) and lists the considerations a court weighs before recognizing an exception, including how foreseeable the harm was, how closely the conduct connects to the injury, the moral blame attached to the conduct, the policy of preventing future harm, the burden on the defendant and the community, and the availability of insurance.

One limit the sources note: the California Supreme Court held in the Southern California Gas Leak Cases (2019) that the defendant owed no tort duty to protect against purely economic losses, meaning money losses that do not grow out of an actionable physical, emotional or reputational injury to a person, or out of physical damage to property.

Reasonable care under CACI No. 401

CACI No. 401 gives jurors the working definition. Negligence is a lapse in the reasonable care needed to keep people, including oneself, from harm. It comes in two forms: an act that a careful person in the same position would avoid, or an omission of something that a careful person would do. Jurors then judge what a careful person would have done in the defendant's place, or the plaintiff's when the plaintiff's own conduct is at issue.

The standard stays fixed while the amount of care it demands moves with the risk. The Sources and Authority quote the California Supreme Court on this point: the level of care that counts as reasonable changes from case to case, but the standard of due care, measured against the danger, does not. Driving through a school zone at dismissal time calls for more caution than the same road at midnight, and the jury measures both against the same reasonable person.

Courts split the work on this element too. The judge sets the standard of care as a legal matter, and the jury measures the facts against it whenever reasonable people could see the conduct differently. Sometimes a statute or regulation sets the standard. California handles that through a separate presumption, covered in our CACI No. 418 explainer on negligence per se.

Instructions that usually travel with 400 and 401

A negligence trial rarely ends with these two. Depending on the case, the judge may add CACI No. 430 on causation, CACI No. 405 if the defendant says the plaintiff's own negligence contributed, CACI No. 406 if the fault of other people is in play, and the damages instructions in the 3900 series. Verdict form VF-400 is the standard special verdict for a negligence claim against one defendant. Our explainers on comparative fault and tort damages pick up those steps.

Questions to sort a negligence claim

• What did the defendant do or fail to do? Write it down as a specific act or omission.
• What would a careful person have done? Note any industry practice, rule or law that speaks to it.
• What harm resulted? Keep medical records, repair bills and proof of lost pay.
• How did the conduct lead to the harm? Map each step between the act and the injury.
• Did anyone else contribute? Other people's fault, including your own, can change the result.

This page explains California's official jury instructions for general readers and is legal information, not legal advice. For a case going to trial, work from the official text and consult a lawyer licensed in California.