What’s wrong with the grammar of this sentence? “Let’s get back to the cakes, quick.” Answer: there’s nothing wrong with it. The sentence comes from Rose Wild’s Feedback column a fortnight ago (she’s referring to The Great British Bake Off). Some readers thought Rose should have used the adverb “quickly” instead of “quick”. I’ll explain why “quick” is fine.
“Quickly” is an adverb and so is “quick”: it’s what’s known as a flat adverb. This is one that has the same form as its related adjective. An example is “first”, which is an adjective (“the greedy columnist ate his