Common law procedure is party-driven. Each side investigates its own case, chooses its evidence, examines and cross-examines witnesses, and argues the law. The judge rules on disputes and delivers judgment but does not, in principle, build the case — a sharp contrast with the inquisitorial tradition, where an investigating judge or dossier-based court takes the lead.
The system's strength is that self-interested parties probe evidence harder than any official; cross-examination has been called the greatest engine for the discovery of truth. Its weakness is that it works only as well as the parties' resources are equal — which is why legal aid, disclosure duties and judicial case-management exist.
Canadian trials are adversarial, tempered by duties the contest does not explain on its own — the Crown's duty to disclose its evidence to the defence (Stinchcombe) chief among them.