be on your guard

"We do not, of course, know exactly why colonial varieties of English around the world have the characteristics that they do ... but we do have very strong evidence that they are as they are because of the way in which people behave linguistically in face-to-face interaction. That is, whole new language varieties, many of them eventually spoken by millions of people, grow and develop out of small-scale contacts between individual human beings."
-Trudgill, Dialects in Contact