Rationale

A. Historical Rationale:

At common law, a criminal defendant’s interest in the case rendered the defendant incompetent to testify as a witness on his own behalf.

B. Modern:

Modern courts have abandoned the common law rule that made a criminal defendant incompetent to testify his own behalf. In an adversary system the burden of proof in a criminal case is on the prosecution; the defendant need not assist the prosecution in any way.