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In the common law, the peremptory pleas (pleas in bar) are pleas that set out special reasons for which a trial cannot go ahead. They are the plea of autrefois convict, the plea of autrefois acquit, and the plea of pardon.
A plea of autrefois convict (Law French for "previously convicted") is one in which the defendant claims to have been previously convicted of the same offence and that he or she therefore cannot be tried for it again. A plea of autrefois convict can be combined with a plea of not guilty.
A plea of autrefois acquit (Law French for "previously acquitted") means the defendant claims to have been previously acquitted of the same offence, on substantially the same evidence, and that he or she therefore cannot be tried for it again. A plea of autrefois acquit can be combined with a plea of not guilty.
Related doctrines include res judicata and, in the criminal context, a plea in bar of double jeopardy. In the plea of pardon, the defendant claims that he or she has been pardoned for the offence and therefore cannot be tried for it.
Under English law, there is an additional peremptory plea, that of special liability to repair a road or bridge. Under English law, local government authorities have the legal obligation to repair roads or bridges; but, in certain circumstances, the responsibility lies with a landowner instead. The local government authority, charged with a failure to repair a road or bridge, can allege that the responsibility lies with a landowner, at which point the proceedings against them are suspended and those against the landowner they allege to have the responsibility are begun; but, if the landowner is found not to be responsible, then the matter may be recommenced against the local government authority. (See R. v. Sutton, Court of King's Bench, 1833)