Definition of ex turpi causa non oritur actio
Ex turpi causa non oritur actio (Latin for "from a dishonorable cause an action does not arise") is a legal doctrine which states that a claimant will be unable to pursue a cause of action, if it arises in connection with his own illegal act. Particularly relevant in the law of contract, tort and trusts, ex turpi causa is also known as the "illegality defence", since a defendant may plead that even though, for instance, he broke a contract, conducted himself negligently or broke an equitable duty, nevertheless a claimant by reason of her own illegality cannot sue.
In the law of tort, the principle would prevent a criminal from bringing a claim against (for example) a fellow criminal. In National Coal Board v England Lord Asquith said,
"If two burglars, Alice and Bob, agree to open a safe by means of explosives, and Alice so negligently handles the explosive charge as to injure Bob, Bob might find some difficulty in maintaining an action against Alice."
It is not absolute in effect. For example, in Revill v Newberry an elderly allotment holder was sleeping in his shed with a shotgun, to deter burglars. On hearing the plaintiff trying to break in, he shot his gun through a hole in the shed, injuring the plaintiff. At first instance, the defendant successfully raised the defence of ex turpi to avoid the claim. However, the Court of Appeal allowed the plaintiff's appeal, holding that the defendant was negligent to have shot blindly at body height, without shouting a warning or shooting a warning shot into the air, and that the response was out of all proportion to the threat.
The precise scope of the doctrine is not certain. In some cases, it seems that the illegality prevents a duty of care arising in the first place. For example, in Ashton v Turner the defendant crashed a car in the course of getting away from the scene of a burglary, injuring the plaintiff. Ewbank J held that the court may not recognise a duty of care in such cases as a matter of public policy. Similarly, in Pitts v Hunt the Court of Appeal rationalised this approach, saying that it was impossible to decide the appropriate standard of care in cases where the parties were involved in illegality.
In other cases, the courts view ex turpi as a defence where otherwise a claim would lie, again on grounds of public policy. In Tinsley v Milligan Nicholls LJ in the Court of Appeal spoke of the court having to "weigh or balance the adverse consequences of granting relief against the adverse consequences of refusing relief". The plaintiff was ultimately successful in Tinsley v Milligan in the House of Lords, which allowed the claim on the grounds that the plaintiff did not need to rely on the illegality.
The recent case of Gray v Thames Trains upheld the basic rule of public policy that disallowed recovery of anything stemming from Plaintiff's own wrongdoing.
- Hewison v Meridian Shipping Services Pte Ltd  EWCA Civ 1821
- Moore Stephens v Stone Rolls Ltd  UKHL 39
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