The word “estoppel” is derived from Old French, literally meaning “stoppage.” The law of equity, or fairness, has developed several estoppel doctrines to deal with situations people find themselves in when one person relies upon another person’s conduct or words. The doctrines are estoppel by conduct or representation, estoppel by deed, promissory estoppel, and proprietary estoppel.
Proprietary estoppel relates to land and has these essential elements. An equity arises between two people when an owner of land (“A”) induces, encourages or allows the person claiming the estoppel (“B”) to believe that B has or will enjoy some right or benefit over A’s property. In reliance upon this belief, B acts to his or her detriment to the knowledge of A. A then seeks to take unconscionable advantage of B by denying the right or benefit which B was expecting to receive. An example is when A says to B: I will give you a deeded right of way over my land if you do not oppose my township application for rezoning of the land which B was intended to oppose. B agrees. The application is granted and A refuses to grant the deeded right of way.
A different kind of estoppel is an estoppel per rem judicatam. This is an estoppel applied in the court system and the Latin phrase literally means “it has passed into a matter adjudged.” A plaintiff may only sue once in the court system for each case. He or she must bring forward the entire subject matter of the case at one time and claim every court remedy which flows out of the subject matter of the case. There is no opportunity to sue in a second lawsuit for something that was inadvertently or intentionally left out of the first lawsuit. This estoppel doctrine is usually called the doctrine of res judicata. The plaintiff is “estopped” (stopped) from launching a second lawsuit. The doctrine also applies to the defendant. He or she must bring forward every defence based on the subject matter of the plaintiff’s case at one time and any related counterclaim to the plaintiff’s claim.
The doctrine of res judicata is a fundamental doctrine of the justice system in Canada and it is based on two traditional policy considerations: firstly, the ground of public policy that it is in the interest of the public that an end be put to litigation, and secondly, the ground of individual right that no one should be twice vexed by the subject matter of the lawsuit. Other considerations include the courts’ scarce resources and the additional financial burden to the litigants.