Trong một câu văn, 2 hay nhiều ý tưởng có cùng đặc tính được gọi là “parallel” (song song). Để câu văn có hiệu quả tốt, chúng ta cần phải viết (hay nói) những ý tưởng song song theo công thức sau đây: danh từ đi với danh từ, vô định với vô định (infinitive), mệnh đề phụ với mệnh đề phụ, v.v…
1. Danh từ song song
They studied history, mathematics, and chemistry.
Nhưng câu sau đây thì không chuẩn: They studied about the past, mathematics, and how matter is constituted.
He learned to swim, to play tennis, and to ride a horse.
Chứ không phải: He learned to play tennis, swimming, and the art of horseback riding.
3. Mệnh đề
In her praises of the summer camp, she mentioned that the food was good, that the climate was perfect, and that the equipment was superb.
Không nên viết: In her praises of the summer camp, she mentioned that the food good, that the climate was perfect, and what superb equipment they had.
Nên: The old house was battered by the rain and bleached by the sun.
Không nên: The old house was battered by the rain and there was no color left because it was standing in the open sunlight.
3. Cố gắng viết những câu văn song song sao cho số từ tương đương nhau
Không nên: He was a good scientist, but was very poor in keeping books.
Sửa lại cho chỉnh hơn: He was a good scientist, but a poor bookkeeper.
Câu này cũng không chuẩn mấy: He believed in democracy for the upper classes, but felt that the common people should be ruled by their superiors,
và nên sửa lại như: He believed in democracy for the upper classes, but autocracy for the masses.