Why do lawyers have primary responsibility for presenting evidence in common-law courts?

In common-law courts, lawyers bear the primary responsibility for presenting evidence because these systems operate under an adversary procedure. Unlike inquisitorial systems, where a judge actively investigates the facts, the adversary system relies on the opposing parties to conduct their own investigations and present information that supports their respective cases.123

This division of labor is based on the principle that a just outcome is most likely to be achieved when an impartial adjudicator—such as a jury or a judge acting as a neutral referee—is presented with all possible relevant information, both incriminating and exonerating. Self-interest motivates the prosecution and the defense to thoroughly gather and present evidence beneficial to their side.31

In this framework, the judge’s role is restricted to ensuring that proper legal procedures are followed, such as enforcing rules of evidence and barring inadmissible information. The judge generally only intervenes to ask supplementary questions if the parties have failed to clarify essential points of law or fact.3412