The words “that” and “which” are often used interchangeably. That’s a big mistake.
Which of the following is/are correct in scientific writing?
The replies which came from five students were transcribed and translated.
The replies that came from five students were transcribed and translated.
The replies, which came from five students were transcribed and translated.
The replies, which came from five students, were transcribed and translated.
These sentences contain “relative clauses” after the subject “The replies” and before “were transcribed and translated”. A clause is a phrase with a verb, and the relative clauses above relate to and say more about “The replies” using the relative pronouns “that” or “which”. Although (1) and (2) mean the same for some writers, (1) should be avoided because it could have two meanings: either (2) or (4).
Use “that” if you want to define the noun by giving specific details. In (2), “The replies that came from five students…”, the writer is implying there were also replies from other people (for example, teachers) or from other students (for example, groups of three, four, or six students). Only the replies from the group of five students were transcribed and translated. The clause “that came from five students” helps to identify the specific “replies” and is a defining clause or restrictive clause.
Use “which” with a pair of commas to give additional information. In (4), “The replies, which came from five students,…”, the relative clause within the commas could be deleted without changing the message (“The replies…were transcribed and translated.”). The clause “which came from five students” is a non-defining clause or non-restrictive clause. The writer is simply telling us more about the replies, and there are no other replies.
Option (3) is missing the second comma, after the non-defining relative clause. You need both commas, as shown in (4). However, one comma before “which” can be used for a non-defining clause at the end of a sentence after an object (“We transcribed and translated the replies, which came from five students”).
Which of these alternatives is correct?
We need to (1) practice / (2) practise deciding between “that” and “which”.
Both words are pronounced the same. In UK English, (2) is correct because “practice” is the noun but “practise” is the verb (you can remember this by noting the noun “ice” in the spelling of practice). However, in US English, (1) is correct because “practice” is both the noun and verb.
Grammar and punctuation are among the top reasons for being rejected by a journal. To ensure the language in your manuscript is publication-ready you should have a native-English-speaking expert in your field edit for grammar, clarity, and accuracy of scientific expression.