The tort of interference with contractual relations has its roots in the tort of inducing breach of contract. It is also refered to as the tort of interference with economic relations. Both the tort of interference with contract relations and the tort of interference with prospective contract or business relations involve basically the same conduct - in one case the interference takes place when a contract is already in existence, in the other, when a contract would, with certainty, have been consummated but for the conduct of the wrongdoer.
The act of inducing the breach must be an intentional one. If the actor had no knowledge of the existence of the contract or his actions were not intended to induce a breach, he cannot be held liable though an actual breach results from his lawful and proper acts. It is not enough that the actor intended to perform the acts which caused the result -- he or she must have intended to cause the result itself. The claim only be asserted against a stranger to the contractual relationship, if the person complained of was a party to the contract, the claim should be brought as a breach of contract claim. Proof that it is reasonably probable that the lost economic advantage would have been realized but for the defendant's interference is required to prevail on the claim.