This section is from the book "The Law Of Real Property and Other Interests In Land", by Herbert Thorn Dike Tiffany. Also available from Amazon: A Treatise on the Modern Law of Real Property and Other Interests in Land .
The duration of the term must appear with certainty from the lease creating it.90 Otherwise it is insufficient to create an estate for years, and the person to whom the lease is made will be either a tenant at will or a periodic tenant91 or if the lease is executed with such formalities as are necessary for the creation of a freehold estate, he may be a tenant for life.92 The lease need not, however, actually name the period during which the tenancy is to endure, but it
87. Petroleum Co. v. Coal, Coke & Manufacturing Co., 89 Tenn., 381, 18 S. W. 65; Sennett v. Bucher, 3 Pen. & W. (Pa.) 392; Wilcox v. Bostick, 57 S. C. 151, 35 S. E. 496.
88. Doe d. Parsley v. Day, 2 Q. B. 147; Cleveland v. Boice, 21 U. C. Q. B. 609; Frull v. Granger, 8 N. Y. 115; Becar v. Flues, 64 N. Y. 518; Whitney v. Allaire, 1 N.
Y. 305, 4 How. Prac. 447. See Adams Ejectment 60, Berrington v. Casey, 78 111. 317.
89. Adams, Ejectment, 12.
90. Say v. Smith, Plowd. 272; Reed v. Lewis, 74 Ind. 433, 39 Am. Rep. 88; Melhop v. Meinhart, 70 Iowa 685, 28 N. W. 545; Corby v. McSpadden, 63 Mo. App. 648.
91. Post Sec.Sec. 61(b), 64(b).
92. Ante Sec. 32.
11.8 Real Property. [ Sec. 46 may fix such period by reference to some collateral fact or event, if the reference is such as to enable the duration of the term to be ascertained at any time. So a lease for as many years as a person named has in other property,93 or "during the minority of B," a living person whose age is ascertainable94 or until certain fixed yearly payments amount to a sum named95 operates to create an estate for years. But a lease creating a tenancy to endure until a particular event occurs, the time of which occurrence cannot be ascertained beforehand, does not create an estate for years. If it did, a lease for life would create an estate for years, since so soon as the life ceases, the duration of the tenancy is known.96 Accordingly a lease for so many years as the coverture between A and B shall continue97 for so long as a certain business may be carried on by the lessee98 or until the premises are sold,99 does not create a tenancy for years. Such a lease would ordinarily create a tenancy for life or in fee simple, subject to a special limitation,1 or, if lacking the formalities necessary for the creation of a freehold estate, it would create a tenancy at will subject to a special limitation.2