There are many ways in which Brits and Yanks express the degree to which they do, love, hate, esteem, disparage, or qualify something in ways that differ only by a word or two. The points of difference are all adverbials, that is, single words or expressions that modify a verb or modify another modifier. Many of these adverbials can be called intensifiers because they serve to make the meaning of the word they modify stronger, just as “a bunch” does with “thanks.”
As a point of departure, I’ll begin with something I’m pretty sure about: If you use the expression “pretty sure,” there’s a two-to-one chance that you’re an American, or under the influence of American English. The expression occurs in most varieties of English, but Americans are more likely to be pretty sure—or to remark that something is pretty good, pretty cool, or pretty darn close—because pretty is the intensifier of choice in informal American English. Why is this?