Literary parodies do not reveal anything about the then relationship of Irish to English, the spread of English and the regional input from England. There were no censuses before 1851 which gave data on speakers of Irish and English. Adams (1965) is a useful attempt to nonetheless produce a linguistic cartography of Ireland at the beginning of the early modern period. The upshot of this situation is that there is no reliable data on the language shift which began in earnest in the early 17th century and which had been all but completed by the late 19th century.

It is clear that the Irish learned English from other Irish who already knew some, perhaps through contact with those urban Irish who were English speakers, especially on the east coast and through contact with the English planters and their employees. This fact had consequences for the nature of Irish English. Bliss (1977) pointed out that this fact is responsible for both the common malapropisms and the unconventional word stress found in Irish English. However, the stress pattern in verbs with final long vowels, e.g. distribute  , educate [edju^Ike:t] , can also be due to English input, particularly as late stress is a feature of southern Irish, not of the west and north, and so influence due to contact with Irish could only be posited for the south of Ireland.

Another point concerning the language shift in Ireland is that it was relatively long, spanning at least three centuries from 1600 to 1900 for most of the country. The scenario for language shift is one where lexical transfer into English is unlikely, or at least unlikely to become established in any nascent supraregional variety of English in Ireland. Such dictionaries as Ó Muirithe (1996) and to a lesser extent Dolan (1998) seem to reveal a large number of Irish loans in present-day Irish English. But the question of currency is the key issue here: there is a great difference between the vocabulary of an older agricultural generation (which is frequently reflected in the entries in these dictionaries) and a younger urban one.

In phonology and syntax the matter is quite different. Speakers who learn a language as adults retain the pronunciation of their native language and have difficulty with segments which are unknown to them. A simple case of this would be the substitution of English dental fricatives by stops (dental or sometimes alveolar, depending on region) in Irish English. A more subtle case would be the lenition of stops in Irish English, e.g. cat [kæt], which, while systemically completely different from lenition in Irish, could be the result of a phonological directive applied by the Irish learning English to lenite elements in positions of maximal sonority.