Rule 601. General rule of competency; disqualification of witness.

(a) General rule. - Every person is competent to be a witness except as otherwise provided in these rules.

(b) Disqualification of witness in general. - A person is disqualified to testify as a witness when the court determines that the person is (1) incapable of expressing himself or herself concerning the matter as to be understood, either directly or through interpretation by one who can understand him or her, or (2) incapable of understanding the duty of a witness to tell the truth.

(c) Disqualification of interested persons. - Upon the trial of an action, or the hearing upon the merits of a special proceeding, a party or a person interested in the event, or a person from, through or under whom such a party or interested person derives his or her interest or title by assignment or otherwise, shall not be examined as a witness in his or her own behalf or interest, or in behalf of the party succeeding to his or her title or interest, against the executor, administrator or survivor of a deceased person, or the guardian of an incompetent person, or a person deriving his or her title or interest from, through or under a deceased or incompetent person by assignment or otherwise, concerning any oral communication between the witness and the deceased or incompetent person. However, this subdivision shall not apply when:

(1) The executor, administrator, survivor, guardian, or person so deriving title or interest is examined in his or her own behalf regarding the subject matter of the oral communication.

(2) The testimony of the deceased or incompetent person is given in evidence concerning the same transaction or communication.

(3) Evidence of the subject matter of the oral communication is offered by the executor, administrator, survivor, guardian or person so deriving title or interest.

Nothing in this subdivision shall preclude testimony as to the identity of the operator of a motor vehicle in any case.