Explanation of leasehold sales, rack rents, 3 lifetime leases??

To answer your question fully would be a huge task. I can recommend “Researching Farming ancestors in Ireland” by Dr William Roulston if you want a detailed study. 

Throughout the eighteenth century leases for three lives were in fairly widespread use. These leases were often for a term of years [usually 31 or 41 years] or for three lives, whichever was the longer. A three-lives lease expired when all the three persons named in the lease had died. This explains why some eighteenth-century leases lasted well into the nineteenth century. Tenants often named young relatives in the hope that at least one of them would survive for many years. In certain instances it was quite difficult to ascertain whether a particular life in a lease had expired, the most common difficulty being a person who had emigrated in the early part of the nineteenth century.

In the case of perpetuity leases [three-lives for ever] a new life could be inserted at the fall of each life on payment of a renewal fine (fee) which was usually half of the annual rent payment. The annual rent, however, never changed and those in possession of such a lease often sublet their land in the latter years of the eighteenth and the early years of the nineteenth century at a substantial profit. These types of leases were very common on the Phillips estate at Limavady and the Vintners estate at Bellaghy, both properties that had been bought by William Conolly, the Speaker of the Irish House of Commons in 1699 and 1729 respectively. Effectively perpetuity leases were freeholds and entitled the holder of the lease to a vote. This was one of the reasons why Speaker Conolly granted freeholds on his estates.

Three-lives leases are very useful for genealogists because, as mentioned above, a tenant often named members of his family (particularly sons and grandsons) as the lives. When new lives were inserted details of age and relationship were often included and it is possible to work out when the old life died. Unfortunately estate records rarely include the names of any sub-tenants. Some 3 lives leases included Royalty, as one of the lives, as they were generally expected to live a long time.

Source: http://www.billmacafee.com/estates/landedestaterecords.htm

See also: http://www.irishabroad.com/yourroots/expert/landrecords.asp

In modern usage, a rack rent is usually a rent that represents the full open market annual value of a holding, often simply called the market rent. Less frequently, a rack rent may also be "the maximum rent permitted by law", or an extortionate rent.

Labourers rarely bought leases. They might, if they had any money, but often they had “at will” arrangements which meant they could move without notice (or be moved without notice). Obviously they had no security of tenure, but equally they were left free to move to follow the available work. They usually rented from the local farmer rather than a superior landlord, though there are some exceptions to that.

Thanks Elwyn, your information does help, I'll look for the source you gave

Elwyn:

Great response!

Roger