When a landowner grants someone permission to use her land, the owner is granting a license. A license may be created by express permission or by acquiescence. The owner generally retains the right to revoke that license at any time. The landowner may nevertheless be estopped from revoking that license—and the license will accordingly become an irrevocable license for “so long a time as the nature of it calls for”—if the person using the land has “expended money or its equivalent in labor” improving the land in the execution of the license. Critically, however, the expenditure of money or labor can make a license irrevocable only if that expenditure is “ ‘substantial,’ ” “considerable” or “great.”
In Lilli Shoen v Juliet Zacharias, two neighbors live at the base of a hill, their backyards running up the steep hillside. Part way up there was a flat spot on either side of the property line. The defendant Zacarias thought the flat spot was entirely on her property, and made some improvements:
(1) brought in contractors to grade the patch to make it flatter,