Bar, plea in, a pleading showing some ground for barring or defeating an action at Common Law. A plea in bar was therefore distinguished from all pleas of the dilatory class, as impugning the right of action altogether, instead of merely tending to divert the proceedings to another jurisdiction, or suspend them, or abate the particular writ or declaration. It was, in short, a substantial and conclusive answer to the action. It followed from this property, that, in general, it must either deny all, or some essential part of, the averments of fact in the declaration, or, admitting them to be true, allege new facts which obviated or repelled their legal effect. In the first case the defendant was said, in the language of pleading, to traverse the matter of the declaration; in the latter, to confess and avoid it. Pleas in bar were consequently divided into (1) pleas by way of traverse, and (2) pleas by confession and avoidance.
In Equity, a plea in bar was a defence resorted to when there was no defect apparent on the face of the plaintiff's bill, alleging affirmative matter, and reducing the case to a particular point, seeking to displace the plaintiff's equity. See now DEFENCE.
In Scottish criminal practice the expression denotes these preliminary pleas which, if sustained, prevent the trial proceeding. The more important of them are: that the accused is under eight years of age; that he is presently insane; that he has 'tholed an Assize,' i.e., that he has already been tried for the same offence; that the Court has no jurisdiction.