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Why We Diagram Sentences

If asked, “Why do we teach the diagramming of sentences?” I suppose the simplest answer is to communicate well and to think properly.  

We communicate well in writing when a sentence means what we want it to mean.  We fail in this if the words aren’t spelled correctly, are written illegibly, or are put together in such a way as to have more than one possible meaning.  The correction of the first two reasons are topics for another time.  The third reason – the proper construction of a sentence – is what diagramming helps to correct. 

A sentence is like a jigsaw puzzle.  If the pieces don’t fit properly, you won’t get the right picture.  Diagramming shows us whether our pieces “fit” as they should.   Wilson Follett said, “No one should ever have to read a sentence twice because of the way it was put together.”  You may read it a few times to ponder it; you may read it a few times because of the beauty or aptness of the thought; but you should not have to read it twice to figure out what it means. 

As an example, we’ll start with a simple “subject – verb – direct object” sentence:  Edgar cooked bacon.  The diagram looks like this: 

Now I add an “indirect object” (the person or thing that receives the direct object): 

Edgar cooked his mother bacon.   

And the diagram looks like this: 

Now I add a prepositional phrase: Edgar cooked his mother bacon in his pajamas. 

Here we stumble and perhaps chuckle.  Was the bacon wrapped in pajamas on the stove?  It takes us a second (or third) reading to figure out that it was Edgar who was in his pajamas, and not the bacon.  A bad sentence.  If we diagram the sentence, we see that “in his pajamas” should modify “Edgar” and would be placed under it. 

So we rewrite our sentence: Edgar, in his pajamas, cooked his mother bacon. A good sentence. 

When we misplace elements of a sentence, such as phrases or clauses, or muddle our pronouns and antecedents, then we have confusion; often humorous confusion.  Here are samples from church bulletins: 

  • Remember in prayer the many who are sick of our church and community. 
  • The ladies of the church have cast off clothing of every kind and they may be seen in the church basement Friday. 
  • For those of you who have children and don’t know it, we have a nursery downstairs. 

You get the idea.  Before we write, we know (or think we know) what we want to say.  We have the idea in our mind, and we put down the words that are in our head.  We know what we are (supposed to be) saying, and so the sentence may make sense to us, but because of haste, or poor grammar, or faulty thinking, the actual sentence isn’t really saying what we intend.   A diagram is like a blueprint or an itinerary for a sentence.  With it, we plan our sentence so that it functions properly and we get to where we want to go.  

The English language is a beautiful thing, but it has drawbacks, one of which is the importance of word order.  We make sense of a sentence because we know (or think we know) what the words are doing; that is, what part of speech the word is. We know (or think we know) when a particular word is a noun, or an adjective, or a verb, etc.  If  it is a noun, we know (or think we know) that it is a subject, a predicate nominative, a direct object, indirect object, or object of a preposition.  If it’s an adjective, we know (or think we know) what it is modifying.  The same holds true for the rest of the parts of speech.  We (think we) know what it is, and we (think we) know what it is doing.  

In English, however, the same word can be different parts of speech, and can be doing different things.  For example, if asked what part of speech the word “swimming” is, many would say, “A verb.” This is true only if it were used with another verb (called a “helping verb”) as in “Edgar is swimming.” By itself, “swimming” could be a noun: “Swimming is good exercise.” (And, as a noun, it could be a subject, a direct object, etc.)  “Swimming” could also be an adjective as in “Our house has a swimming pool.” It could also be a participle:  “I saw a duck swimming in the lake.” 

You see, what part of speech a word is, and how it is being used as that part of speech, is tied to word order.  If the words are out of order, so is your sentence.  

Here are some other examples where not knowing what part of speech a word is, or putting it in the wrong order, can be confusing: 

  • Driving home last night, a deer came out of the woods.  I wonder where the deer got its driver’s license? 
  • In the parking lot, I found a silver woman’s watch.  That must be some glittering woman. 
  • The mother watched her son drive off through the window.  Call the insurance company!

 If we go back to that third sentence – Edgar cooked his mother bacon in his pajamas – many would say, “Well, of course I know the bacon wasn’t in the pajamas.”  But that’s like the error in poor penmanship when the student says, “Well, of course, that’s an “i” and not an “e” or a “t” and not an “l.”  The student may think so, but the penmanship (or, with the misplaced prepositional phrase, the construction of the sentence) says differently. 

This brings up a second reason, and perhaps more important, reason to diagram sentences: to think correctly.  A sentence is the expression of a thought. Therefore, the rules that govern the construction of a sentence (i.e., grammar) are the rules of thought.  As G. K. Chesterton said, “Most statements that are unreasonable are really ungrammatical.”  Even though a sentence can mean what we want it to mean, what we want it to mean may not make sense. Poor grammar leads to sloppy thinking. 

Perhaps a good contemporary example of this is the oft heard statement, “Truth is relative.” A simple sentence to diagram:

The “backslash” after the verb is like a grammatical “equal” sign, so the statement is saying “truth” and “relative” are the same thing.  Yet any reasonable definition of “truth” (e.g., “conformity with reality”) cannot equate with any reasonable definition of “relative” (e.g., considered in relation to something else”).  As Chesterton also said, “If truth is relative, to what is it relative?” 

Incidentally, this is one reason why we require the study of Latin.  Because of its “case system” (the bane of every Heights’ student), Latin “reverses” the process. Word order is fluid, but the very spelling of a noun changes if it is the subject, a direct object, an indirect object, or the object of a preposition.  The spelling of a pronoun changes depending on its role and its antecedent.  Adjectives (including articles and participles) change spelling depending on what they modify.  This causes grief and tears to our boys, but it forces them to know what is going on in a sentence.  

Most lawyers will tell you that many cases are argued, not because of a sense of “right or wrong,” but because of a disagreement about what a law means. And the reason they argue is because the law was written poorly.  If Congress had to diagram a law before it was passed, we’d have fewer laws (a good thing) and better laws (a very good thing). 

“It is difficult to believe,” said Chesterton, “that people who are obviously careless about language can really be very careful about anything else.” We diagram so as to be careful with our sentences, and we are careful with our sentences so as to be careful with our thoughts. These are very useful things.  

About the Author

Robert Greving

Latin, English

Robert Greving has been a member of the faculty at The Heights since 1999. Mr. Greving served five years in the U.S. Army J.A.G. Corps.  Originally from North Dakota, Mr. Greving earned a B.A. in history at Louisiana State University.

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