An early court hearing at which a judge decides whether there is enough evidence for a case to proceed - the defence's first real look at it.
A preliminary hearing - called a preliminary examination or a probable cause hearing in some places - is a hearing in open court at which a judge decides whether the prosecution has enough evidence for the case to go forward. It is the alternative route to a grand jury indictment, and in the many states that use it, it is the first occasion on which the evidence is tested by anyone outside the prosecution.
What it is not is a trial. The judge is not deciding guilt, the standard is probable cause rather than proof beyond a reasonable doubt, and the prosecution need only put forward enough to clear that bar - which usually means a fraction of its evidence, often through a single officer. The defence may cross-examine and may in principle call evidence, but a defendant rarely testifies, because anything said is on the record for the rest of the case.
Its practical value to the defence is usually informational rather than dispositive. Cases are dismissed at this stage sometimes, and charges are reduced more often, but the reliable benefit is that a witness gives sworn testimony early, on a transcript, which can be used later if their account changes. That is also why the hearing is frequently waived: where the outcome is not in doubt and negotiations are under way, some defendants give it up, occasionally in exchange for something concrete. Waiving it is a decision with consequences that should be made on advice rather than by default.
Whether there is a preliminary hearing at all depends on the jurisdiction and often on the seriousness of the charge. Where a grand jury has already returned an indictment, there is generally no preliminary hearing, because the charging decision has been made; that is a common reason a hearing that had been scheduled does not occur.
This is the hearing at which a defence lawyer learns what the case actually consists of, and that is worth more than the low probability of a dismissal. If there is a decision to make about waiving it, the question to ask is what is being received in return and whether the testimony being given up would have been useful later. Family and friends can help by attending and by noting who gave evidence and what was said; the transcript is the formal record but is not always obtained quickly, and knowing what to order matters.
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