Final answer:
Yes, the plaintiff in a civil action must prove his case by a preponderance of the evidence.
Step-by-step explanation:
In a civil action, the plaintiff does have to prove his case by a preponderance of the evidence. This means that the evidence presented must weigh more on the plaintiff's side in the eyes of the jury or judge. The standard of evidence in a civil case is lower than that of a criminal case, where the state must prove its case beyond a reasonable doubt.