That vs. which. Which often follows a comma and introduces a phrase that provides additional information not essential to the meaning of the sentence. That introduces a phrase that is essential to the meaning of the sentence.

The report, which is twenty pages long, is mandatory reading. (Which introduces additional, but unnecessary, information.)

The report that is twenty pages long is mandatory reading. (That points out a characteristic of the report and distinguishes it from a ten-page report.)


Words of the day

tome [countable]

  • Meaning: literary a large heavy book
  • e.g., What is easier to read: a newspaper or a law tome?

piz‧zazz [uncountable]

  • Meaning: (informal) something that has pizzazz is exciting and has a strong interesting style:
  • e.g., Their new album has plenty of pizzazz.
  • e.g., Now is the time to create a marketing program full of energy and pizzazz.

Written by Shengdong Zhao

Shen is an Associate Professor in the Computer Science Department, National University of Singapore (NUS). He is the founding director of the NUS-HCI Lab, specializing in research and innovation in the area of human computer interaction.