Sentence 3 introduces the topic under discussion i.e Rationalism and beauty 5 takes the idea forward by providing the historical backdrop 52 make a mandatory pair as the pronoun “this" in 2 has been defined in 5 21 also make a mandatory pair as the phrase any such theory" in 1 has been defined in 2.4 explains the ideas mentioned in 1 Hence 14 also make a mandatory pair.