Just like easements, joint tenancies also require four elements which lawyers call the "four unities" suggesting that they must co-exist at a same moment of time:

  • Unity of interest: the interest of each joint tenant must be identical in nature, duration and extent.
  • Unity of title: the interests must arise from the same document.
  • Unity of possession: each joint tenant must have an equal right to occupy or possess the entire property, none holding any part separately to the exclusion of the others. The fee simple is owned by all joint tenants.
  • Unity of time: the interests of the joint tenants must arise or "vest" at the same time.

To survive, once created, the unities of title, interest and of possession must continue to exist.

Joint tenancy has been described by one Canadian lawyer as "a game of Russian roulette." This is because of the most important characteristic of all: when one joint tenant dies, his (or her) interest goes to the remaining joint tenant. In this way, by the passing deaths of all but one joint tenant, the title is finally unified with the last survivor. Lawyers call this the "right of survivorship." This characteristic prevents an interest held in joint tenancy from being conveyed by will. This precarious legal device is not as common today as it once was, confined, now, primarily to family property, where spouses might, for the purpose of estate planning, hold real property as joint tenants, or as between co-trustees who are holding title to property.

A tenancy in common, on the other hand, conveys no right of survivorship. When one co-tenant dies, the interest of the defunct co-tenant forms part of his or her estate and can be conveyed to a next-of-kin. The only "unity" required for a tenancy in common is the unity of possession: all tenants in common are allowed to possess the land so held equally. No tenant in common has a seperate part of the property except by partition. Commercial partnerships often provide that partnership property is held in common between the partners. The same is true for condominium common areas such as stairs and entrance lobbies.

Historically, common law and equity courts have waged a battle over a preference for joint tenancies or tenancies in common. The common law courts favoured joint tenancies whereas the equity court, the tenancy in common. In modern times, the common law courts, too, came to lean more towards a tenancy in common. "The subtlest indication that property was meant to be held in common would suffice to overcome (the presumption of a joint tenancy," writes Professor Bruce Ziff of the University of Alberta in Principles of Property Law (1993). In fact, even the use of the word "jointly" is not necessarly conclusive of an intent to establish a joint tenancy provided the signatories intended the word to have its ordinary rather than technical meaning (Sellon v. Huston Estate (1991) 107 NSR 6 and Central Trust v. McCann Estate (1987) 59 Ontario Reports 488).

Also from the law reports, the following words have caused the courts to construe a tenancy in common:

  • "equally among them"
  • "equally"
  • "in equal moieties"
  • "share and share alike"
  • "respectively"
  • "as they shall severally die"
  • "to each of their respective heirs"
  • "between"
  • "amongst"
  • "each"
  • "all to have part and alike every one of them to have as much as the other"

The argument is now moot in some provinces which have enacted conveyancing or property legislation which provides that there is a presumption of a tenancy in common "unless an intention sufficiently appears on the face of the will." Therefore, in some provinces, if it is the intention to create by will a joint tenancy, a testator will be advised to choose his or her words carefully. The existence of a statutory presumption in favour of a tenancy in common also adds a new essential ingredient to the four unities: express intention: clear words which refer to a joint tenancy, or else you run the risk of a court deciding that you really meant a tenancy in common.

The Ontario case of McEwen v. Ewers and Ferguson (summarized in the Canadian Real-Estate Law Case Book) noted that the provincial Conveyancing and Law of Property Act had reversed the common law presumption, to now favour the tenancy in common. The words "to my daughters ... jointly and should they decide to sell the said property each of them is to have an equal share of the proceeds of the said sale" were interpreted to be a tenancy in common. The court said: "where the words "jointly" and "equally" have been used the courts have held the gift a tenancy in common. Also, that where there are words of division or distribution such as "to be divided" or "equally" it created a tenancy in common. Further, that the use of the word "share" or similar words also import a tenancy in common."

Besides the accruing of the entire estate into the last survivor, a joint tenancy can also be extinguished by severance. The leading case is Williams v. Hensman in which three ways were given as causing the severance of the joint tenancy:

  • Action of any of the joint tenants to dispose or sell their share. This type of action breaks down the four unities. If Sue and Sally have a property in joint tenancy, and Sally sells to Bob, Sue and Bob hold as tenants in common. An important distinction, though, is where Sally, Sue and Bob all hold a property as joint tenants, and where Bob sells his interest to Charles, Charles holds as tenant in common, his share passing on to his heirs. Sally and Sue continue as joint tenants between themselves.

    The action of conveying to oneself, where permitted under provincial conveying legislation, can also cause conversion of a joint tenancy to a tenancy in common as was noted in the case of Murdoch v. Barry as can a mortgage taken by one of the joint tenants in those provinces where the registration of a mortgage transfers title to the lender. These acts do not require the consent of the other co-tenant(s).

  • Mutual agreement amongst the joint tenants to sever. This is justified under equity law under the maxim that "equity regards as done that which ought to be done." Professor Ziff, in his Property Law book referenced above, suggests that "a sale or lease by all joint tenants does not result in a severance, without more, because this arrangement is consistent with the continuation of joint ownership in the proceeds of sale or in the newly-acquired property. It follows that an agreement to sell at some future time will not transform the nature of the co-ownership." Other authors have suggested that the granting of an easement does not cause severance as the unity of title survives.
  • Any course of dealing sufficient to intimate that the interests of all were mutually treated as constituting a tenancy in common. This would include even uncompleted negotiations as was the case in Robichaud v. Watson (summarized in the Canadian Real-Estate Case Law page). But in Morgan v. Davis (1984) 17 Estates and Trust Reports 271, the New Brunswick court said that a court should not lightly infer severance from the mere fact of negotiations. It would "depend upon the particular facts. Canadian courts ... should look for a clearly established intention to sever (and) not be too quick to find a common intention to sever where an agreement ... was ... by mutual consent, not carried out." Again, in Re Sorensen (1977) 90 Dominion Law Reports p. 26, the Alberta Supreme Court said that "the onus to demonstrate that there has been a severance lies in those who so contend." The court acknowledged that mutual wills by all joint tenants "leaving the property to the other" could be construed as sufficient intention to sever but not just one will alone by one of the joint tenants. "The declaration by one party of an intention to sever alone without any other act and without acceptance by the other joint tenants does not sever the tenancy."

There are other ways to sever a joint tenancy, judicial sales and bankruptcy being examples. The murder of one joint tenant by the other is another method of severing the joint tenancy although, in a case called Schobelt v. Barber, the court preferred a to create a constructive trust of the victim's interest.

Most provinces have legislation that allows for a petition to the court for partition of property. In British Columbia, the law is known as the Partition of Property Act. The procedures an criteria for partition is different in each province but they generally all give the court discretion, require that the petitioner be in possession or have an immediate right to possession (see, for example, Garnet v. McGoran where a mortgagee was denied partition based on this criteria), and that partition is preferred over sale.

In Bisson v. Luciani it was decided that a joint tenant or tenant in common had a prima facie right to a partition unless a "sufficient reason" could be found not to partition. With regards to the preference of partition over sale, this is exactly the route the court took in Cook v. Johnston.

A final matter of concern involves the occupation or use by one co-tenant which might result in occupation rent being made payable to the other co-tenants (in common or joint). In Dennis v. McDonald 1981 WLR 810, it was said, on the subject of occupation rent between tenants in common, "that only in cases where the tenants in common not in occupation were in a position to enjoy their rights to occupy but chose not to do so voluntarily, and were not excluded by any relevant factor, would the tenant in common in occupation be entitled to do so free of liability to pay an occupation rent."

The case of Osachuk v. Osachuk was an example where occupation rent was not ordered. The case noted that the common law did not provide for any accounts to be made for rents of joint property unless one co-tenant "expressly undertook to act as bailiff for the other" or "if one joint tenant had ousted the other."