19. Having found the Rent or value of the _usus fructus per annum_, the question is, how many years purchase (as we usually say) is the Fee simple naturally worth? If we say an infinite number, then an Acre of Land would be equal in value to a thousand Acres of the same Land; which is absurd, an infinity of unities being equal to an infinity of thousands. Wherefore we must pitch upon some limited number, and that I apprehend to be the number of years, which I conceive one man of fifty years old, another of twenty eight, and another of seven years old, all being alive together may be thought to live; that is to say, of a Grandfather, Father, and Childe; few men having reason to take care of more remote Posterity: for if a man be a great Grandfather, he himself is so much the nearer his end, so as there are but three in a continual line of descent usually co-existing together; and as some are Grandfathers at forty years, yet as many are not till above sixty, and _sic de cæteris_. 20. Wherefore I pitch the number of years purchase, that any Land is naturally worth, to be the ordinary extent of three such persons their lives. Now in _England_ we esteem three lives equal to one and twenty years, and consequently the value of Land, to be about the same number of years purchase. Possibly if they thought themselves mistaken in the one, (as the observator on the Bills of Mortality thinks they are) they would alter in the other, unless the confederation of the force of popular errour and dependance of things already concatenated, did hinder them. 21. This I esteem to be the number of years purchase where Titles are good, and where there is a moral certainty of enjoying the purchase. But in other Countreys Lands are worth nearer thirty years purchase, by reason of the better Titles, more people, and perhaps truer opinion of the value and duration of three lives. 22. And in some places, Lands are worth yet more years purchase by reason of some special honour, pleasures, priviledge or jurisdiction annexed unto them. 23. On the other hand, Lands are worth fewer years purchase (as in _Ireland_) for the following reasons, which I have here set down, as unto the like whereof the cause of the like cheapness in any other place may be imputed. First, In _Ireland_ by reason of the frequent Rebellions, (in which if you are conquered, all is lost; or if you conquer, yet you are subject to swarms of thieves and robbers) and the envy which precedent missions of English have against the subsequent, perpetuity it self is but forty years long, as within which time some ugly disturbance hath hitherto happened almost ever since the first coming of the English thither.