Mass. Gen. Laws ch. 184 § 7
A conveyance or devise of land to two or more persons or to husband and wife, except a mortgage or a devise or conveyance in trust, shall create an estate in common and not in joint tenancy, unless it is expressed in such conveyance or devise that the grantees or devisees shall take jointly, or as joint tenants, or in joint tenancy, or to them and the survivor of them, or unless it manifestly appears from the tenor of the instrument that it was intended to create an estate in joint tenancy. A devise of land to a person and his spouse shall, if the instrument creating the devise expressly so states, vest in the devisees a tenancy by the entirety.
A conveyance or devise of land to a person and his spouse which expressly states that the grantees or devisees shall take jointly, or as joint tenants, or in joint tenancy, or to them and the survivor of them shall create an estate in joint tenancy and not a tenancy by the entirety. In a conveyance or devise to three or more persons, words creating a joint tenancy shall be construed as applying to all of the grantees, or devisees, regardless of marital status, unless a contrary intent appears from the tenor of the instrument.
A conveyance or devise of land to two persons as tenants by the entirety, who are not married to each other, shall create an estate in joint tenancy and not a tenancy in common.
Mass. Gen. Laws ch. 184, § 7