Legal Definitions - personal knowledge

Personal knowledge refers to information that an individual has acquired directly through their own senses or experiences, rather than through secondhand reports, assumptions, or speculation. In legal settings, a witness is generally only permitted to testify about facts or events of which they have personal knowledge. This means they must have seen, heard, felt, smelled, or otherwise directly perceived the information they are presenting.

• Example 1: Witnessing an Incident

  Imagine a person, Sarah, who was standing at a bus stop and saw two cars collide at an intersection. When called to testify in court, Sarah can describe what she saw: the color of the cars, the direction they were traveling, the sound of the impact, and the immediate aftermath. She can state that she saw the red car run a stop sign. Sarah's testimony is based on her personal knowledge because she directly observed the entire event with her own eyes and ears. She cannot, however, testify about what the drivers might have been thinking or what someone else told her about the accident, as that would not be personal knowledge.

• Example 2: Professional Expertise and Observation

  Consider a certified building inspector, Mark, who conducts a thorough examination of a house for sale. He inspects the foundation, roof, plumbing, and electrical systems. In his report and potential testimony, Mark can detail the specific cracks he observed in the foundation, the water stains he found on the ceiling, and the faulty wiring he identified. Mark's statements are based on his personal knowledge because he personally performed the inspection, used his professional expertise to interpret his observations, and directly perceived the conditions of the house. He cannot testify about what the previous owner *said* was wrong with the house unless he personally verified those claims.

• Example 3: Direct Experience with a Product or Service

  Suppose a customer, David, purchased a new smartphone and, after using it for a week, found that its battery consistently died within a few hours, despite being fully charged. When he contacts customer service or provides a review, David can describe his experience: "I charged the phone fully each night, and by noon, it was always dead, even with minimal use." This statement is based on David's personal knowledge because he directly used the product and personally experienced its performance issues. He cannot claim that "everyone says this phone has bad battery life" unless he is specifically asked about common complaints, as that would be hearsay and not his personal experience.