Wisconsin Statutes Property (Ch. 700 to 710) § 700.02. Classification of interests in property as to duration

(1) A fee simple absolute;

(2) A defeasible fee simple which may be a fee simple determinable automatically expiring upon the occurrence of a stated event, a fee simple subject to a condition subsequent with a power in the transferor or the transferor's successors in interest to reacquire the fee by reason of a breach of the condition, or a fee simple with a remainder over to a person other than the transferor or the transferor's successors in interest to take effect upon the occurrence of a stated event;  for purposes of this subsection, a stated event can be either the happening, or the nonhappening, of a specified occurrence, and can be either certain or not certain to happen;

(3) An interest for life, which may be created for the duration of a life or lives of one or more human beings;

(4) An interest for years, which is any interest the duration of which is described in units of a year or multiples or divisions thereof;

(5) A periodic interest, which will continue for successive periods of a year, or successive periods of a fraction of a year, unless terminated;

(6) An interest at will, which is terminable at the will of either the transferor or the transferee and has no designated period of duration.