In the English law of tort, professional negligence is a subset of the general rules on negligence to cover the situation in which the defendant has represented him or herself as having more than average skills and abilities. The usual rules rely on establishing that a duty of care is owed by the defendant to the claimant, and that the defendant is in breach of that duty. The standard test of breach is whether the defendant has matched the abilities of a reasonable person. But, by virtue of the services they offer and supply, professional people hold themselves out as having more than average abilities. This specialised set of rules determines the standards against which to measure the legal quality of the services actually delivered by those who claim to be among the best in their fields of expertise.