Once upon a time and long, long ago (a few decades back) in a frozen country far, far away (southeast Michigan) business writing was coming out of the fog (there was a push to eliminate unnecessary words and phrasing). Gobbledygook and doublespeak (it WAS around 1984) was out and succinct writing was in. During this time I was an undergrad majoring in English and was instructed to “replace every ‘which’ with ‘that’ and then cut every ‘that’ possible.” While my professor had good intentions, this is so very wrong!
Still, his advice had an impact on my writing style. An author’s voice and style evolves out of sentence structure. It’s related to your word choice and sentence length. In simple terms, how you say what you say. This is one of the most difficult aspect for my writing students to grasp (whether they’re elementary at-risk learners, college students, or budding freelance writers). There is no single, correct way to convey an idea. Instead, we have a multitude of options to get our thoughts across in writing.
While my college professor did help me learn to write succinctly, the question on when (or whether) to use ‘that’ or ‘which’ is an issue of clarity. Each word has a purpose dependent on whether the clause the word is a part of is necessary–or optional–to the meaning of the sentence. Clauses (a group of words with their own subject and verb) add to a base sentence and provide more information. If the information is optional, use ‘which’. If the information is essential, use ‘that’. For example:
Claire selected a green blouse to wear with the grey skirt.
Claire selected a green blouse, which had white buttons, to wear with the grey skirt.
The green blouse that complemented Claire’s eyes made the outfit memorable.
The first sentence is the base sentence. In the second sentence, the clause added to the base sentence is optional. While it adds to the information about Claire and her outfit, it can be removed without being missed. The third sentence expands on the idea behind the first sentence. It includes a clause that offers additional but necessary information about the rest of the sentence; if this clause is removed, we do not understand why the outfit would be memorable. It is an essential clause.
Note that commas surround the non-essential clause: Claire selected a green blouse, which had white buttons, to wear with the grey skirt. Whenever you can remove a clause from the sentence without losing meaning, the clause should be “cradled by commas.” If removing the clause would make the sentence less meaningful or confusing, do not use commas to separate it from the rest of the sentence.
So, when we receive advice to write tightly, it’s not about changing ‘which’ to ‘that’ and then eliminating ‘that.’ It’s about getting your thoughts across with only the words needed. Whenever my college students ask how long their story, essay, article, or research paper should be, my answer is, “As long as is necessary to convey your point.” It’s really a matter of style.