Explain the difference between rhotic and non-rhotic dialects of English.

In rhotic English dialects, the historical English /r/ sound is preserved in all pronunciation contexts. In non-rhotic English dialects, speakers no longer pronounce /r/ in postvocalic environments—that is, when it is immediately after a vowel and not followed by another vowel.  For example, in isolation, a rhotic English speaker pronounces the words hard and butter as /ˈhɑːrd/ and /ˈbʌtər/, whereas a non-rhotic speaker "drops" or "deletes" the /r/ sound, pronouncing them as /ˈhɑːd/ and /ˈbʌtə/.  The rhotic varieties of English include the dialects of South West England, Scotland, Ireland, and most of the United States and Canada. The non-rhotic varieties include most of the dialects of modern England, Wales, Australia, New Zealand, and South Africa.