Both phrases salt and pepper and bacon and eggs are examples of nonreversible word pairs. In other words, these words always come in the same order. These pairs could also be considered strong collocations, or set phrases. Teachers can use the lexical approach to assist students in learning language in 'chunks'. This approach to teaching focuses on learning groups of words, and words and phrases that commonly come together in English. Once you've begun to notice these 'chunks', it's easy to see how learning chunks of language, rather than just single words helps to improve fluency.