Rule 601: Competency to Testify in General

Rule 601 establishes a presumption of competency: every person is presumed capable of serving as a witness. This is a significant departure from common law, which imposed numerous disqualifications based on age, mental capacity, religious belief, criminal conviction, and interest in the litigation.

Under the modern approach reflected in Rule 601, the traditional competency barriers have largely been swept away. Children, persons with mental disabilities, and parties to the litigation are all presumed competent. Issues that previously went to competency — like a witness's age, intelligence, or mental condition — now go to the weight of the testimony rather than its admissibility. The jury can consider these factors in deciding how much credibility to give the witness.

As with privilege under Rule 501, there is a choice-of-law provision for diversity cases. When state law supplies the rule of decision, state competency rules apply. This matters because some states retain Dead Man's statutes, which bar interested parties from testifying about transactions with deceased persons in certain cases.