There is Old English, and there is the English we speak now. When did exactly did the British (or Americans) change from speaking Old English to speaking the current form of English?
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There are considered to be three major eras of English: Old English, Middle English, and Modern English. Old English is a very different language, complete with a different alphabet. Middle English emerged after the Norman conquest of England with influence from French and other continental languages. Modern English emerged a few hundred years later with the Great Vowel Shift. The first few hundred years of Modern English are referred to as Early Modern English, which is well represented in the works of Shakespeare. The current version of English started to coalesce around 1700.
I could go on, but: http://en.wikipedia.org/wiki/History_of_the_English_language
I am just adding some dates for those not familiar with English history.
Old English (before 1066AD) is almost unreadable, with a different grammar and a few extra characters. It is closer to Danish or German.
Middle English (1100-1500AD) is almost readable, but the pronunciation is very different.
Then, Early Modern English starts around 1600; this still sounds old fashioned, but is recognisable if you read the King James bible or Shakespeare.