Swift recognized that “slavery” was an ambivalent term: on one hand, slavery can be seen as a biological imperative—a natural condition of the innately servile; on the other hand, slavery can be seen as a political accident— a circumstance imposed from without by those with the will and power to oppress. Swift consistently characterized the Irish as “slaves” and called the relationship of Ireland to England “slavery.” In the case of the Irish, Swift feared that their slavery, which may have begun as external oppression, would eventually become an intrinsic part of Irish character. If Swift's observations on slavery in Ireland are applied to the slavery of the Yahoos to the Houyhnhnms in Book iv of Gulliver's Travels, the question of whether slavery is a matter of nature or nurture also arises, for there is evidence in Book iv to suggest that the Yahoos were as rational as Gulliver when they arrived in Houyhnhnmland.