Even as someone who deals professionally with written English, there are still some very common words that I have found consistently challenging. English words are used and reused in so many different patterns and contexts that even one that you think you know can give you pause. Especially in the world of scientific papers, where accuracy and specificity are paramount, these ‘similar, but different’ words require special attention to make sure you use them correctly. Two of the worst offenders are which and that. Let us look at these words, their nuances, and the rules you need to know to use them correctly in a sentence.
The Difficulty of Determiners
Among words that are as confusing as they are common, which and that stand head and shoulders above others. This is because both of the words are used as a part of language known as a determiner.
A determiner is a word that precedes a noun to specify the quantity or what the noun refers to. These come in the form of articles (a, an), demonstratives (this, these, those), possessives (your, my, our).
The specific type of determiner role which and that fill is the demonstrative, meaning they express the relationship between a noun and another piece of information. For both which and that, the relationship they describe is one where a context is applied to a previously mentioned subject. But how are they different?
The Clause is Key
The secret to choosing the right word is knowing whether it connects a defining clause or a non-
defining clause to the sentence.
For a defining clause, use that.
For a non-defining clause, use which.
To make it easier to pull these from a sentence, in examples, I’ll be marking the defining clauses in blue and the non-defining clauses in yellow.
A defining clause, also known as a restrictive clause, provides information essential to your understanding of the sentence.
Example:
The group that received the performance-enhancing drug saw great improvements in aerobic capacity.
Here, a distinction is being drawn between the experimental and control groups. There was more than one group, but the group we are concerned with was explicitly the one receiving the drug. If you removed this clause, you would have ‘the group saw great improvements in aerobic capacity’, which does not give the reader enough information to understand the situation. Therefore, it is a defining clause.
A non-defining clause, unlike a defining clause, does not restrict the meaning of the sentence. Rather than providing vital insight and context, it simply adds auxiliary information.
Example:
The flu vaccine, which is currently being experimented with in pill form, has been administered as an injection since its invention in the late 1930s.
In this example, while new and perhaps relevant information is relayed in the clause introduced by which, a complete, specific, and comprehensible sentence exists without that clause. ‘The flu vaccine has been administered as an injection since its invention in the late 1930s’ is an outstanding sentence all on its own. This is what makes it a non-defining clause.
Playing with Which and That
Let us look at a few more instances of which and that in action and see the different ways they can be used when communicating information:
The kilogram is actually a real, physical object, which is located at the International Bureau of Weights and Measures laboratory at Sèvres, France.
As you can see, the non-defining clauses can come in the middle and the end of the sentence.
Scientists found a meteorite that contained a previously unknown titanium sulfide mineral, which they named ‘Wassonite’.
You can even use both words with both types of clauses in a single sentence.
Scientists found a meteorite containing a previously unknown titanium sulfide mineral, later named ‘Wassonite’.
Or use neither and get the same information across. One thing that makes English such an expressive language is the same thing that makes it so difficult. Basically, any phrase can be reworded to avoid using which or that while still being entirely grammatically correct. Often enough, this rewording can be just mean removing the word altogether. Let us look at that first example again:
The kilogram is actually a real, physical object, located at the International Bureau of Weights and Measures laboratory at Sèvres, France.
Side Note: If you need to meet a count for a scientific journal, this can actually be an excellent way to cut down on extraneous words. To learn more about meeting word counts, read my article here.
When it comes down to it, confusion aside, which and that are useful tools that explain the relevance of different bits of information to your reader. You do not have to use them strictly, but they can make it easier for your reader to follow your writing and understand the information you are putting in front of them. To learn more about utilizing the English language tools to create clear, concise, and publishable work, contact me.