Which is that – or is it? This question plagues users of the English language trying to communicate in a more sophisticated fashion. Let’s address this issue by explaining the basics of relative pronouns and then by looking at the two schools of thought driving the choice between that and which.
A pronoun is a word that allows one to reference a previously stated noun without having to repeat the noun. Consider the following:
Martha makes friends easily. She has a fun personality.
In the first sentence, Martha is one of the nouns. The second sentence elaborates further on Martha but, in an effort to avoid redundancy, uses the pronoun “she” instead of Martha.
Why are the pronouns described as relative? Relative simply means that a common element or idea exists between two sentences or phrases. Consider the two following sentences.
Martha is reading a book. The book is on the table.
“The book” relates the two sentences together.
To express the above idea in two, short sentences recalls the simplicity and choppiness of the “See Jack run” books used when learning to read. This works if you are writing children’s books. However, if writing for a more discerning audience, a higher level of sophistication is expected. The correct use of relative pronouns helps writers, print and web writers alike, meet that level of sophistication.
THAT vs. WHICH
The choice between that and which enjoys at least two basic schools of thought.
1. These relative pronouns have their own unique environments which prohibit using one in place of the other.
2. These relative pronouns are interchangeable in the sense that where which is appropriate, that can also be used.
Let’s consider the two schools of thought.
If the clause being embedded inside of another sentence is essential, one uses that. If the embedded clause is non-essential, the relative pronoun is which. Since the appropriate environment hinges on the notion of essential or non-essential, let me explain. Essential means that the additional information of the embedded clause bears real weight on the sentence’s meaning. Non-essential means that the additional information can be removed without compromising the sentence’s meaning.
Here are some examples of essential and non-essential clauses as used with that or which.
I need the map. The map gives directions to the airport.
The map is the common element of both sentences. Because the information in the second sentence references a specific map, the one that gives directions to the airport, the relative pronoun is that. The combined sentence reads:
I need the map that gives directions to the airport.
My son’s jacket fell in the puddle. I just washed the jacket yesterday.
The jacket is the relative concept found in both sentences. In this instance, because the jacket having been washed the day before has no bearing on the jacket ending up in the puddle, the correct relative pronoun is which.
My son’s jacket, that I just washed yesterday, fell in the puddle.
Those espousing the thought that the two relative pronouns are interchangeable would argue that, in the case where the embedded clause is non-essential, one has the option of using either that or which. Note that the overlap of that and which only works with non-essential clauses. If the embedded clause be essential to the meaning of the sentence then that must be used.
Should the common element of the two sentences be a person, then the relative pronoun would be who. However, that has been used in relative clauses dealing with people. For example:
The candidate that is working the crowd hopes to win over the voters.
I began the study of that vs. which with the questioning statement “Which is that – or is it?” The answer depends upon the school of thought one espouses. For some, because which and that are interchangeable, then the statement “which is that” is correct. For those who espouse that each relative pronoun works only in a very specific environment, then “which is that” is not correct. That will always be that, and which will always be which. In the end, consistency is key. Choose your school of thought and then follow it on a consistent basis.