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Lesson 3.3: Identifying Clauses Using Subject-Auxiliary Inversion

downloadable subjects and SAI worksheet


Another cool way to identify subjects is to use Subject-Auxiliary Inversion, which we already saw in Lesson 3.2. There, we saw that one way to turn a statement into a question is to move the auxiliary verb to precede the subject. Not only does this allow us to “discover” the auxiliary verb, but it will also “reveal” the subject. Remember, of course, that we make use of subjects all of the time in our speech, and have no problem doing so. But if we want a trick to consciously find the subject, simply make a question:


    The chicken will eat the corn. → Will the chicken __eat the corn?


The portion of the sentence that the auxiliary verb inverts with or moves around will always be the subject, no matter how long or how short it is.


   Mo is eating carrots. →  Is Mo __ eating carrots?


    The kid with a gigantic hat can’t see his friend.   →  Can the kid with the gigantic hat __ see his friend?


You can have students turn some sentences like these into questions by using SAI.


  The kids should take their lunches on the fieldtrip.

  The teacher visiting from Chicago will be our substitute next week.

  The test on factors could be next week.

  The man who talked with us on the bus about safety could also visit the classrooms.


Subject Auxiliary Inversion (SAI), like Tag Questions, will always pick out the subject of an independent clause, not a subordinate clause, so it will distinguish these from each other. Being able to easily pick out the subjects of our sentences will help ensure


  • that each sentence has a subject, a required element of most academic writing

  • that the subject “agrees with” the verb, if that’s something that you’re concerned about in your students’ writing

  • that each independent clause has only one main subject, if you’re seeing comma splices/run-ons in students’ writing


I want to emphasize, though, that there are good reasons to talk about subjects other than simply dealing with issues in writing. That will come along for free, but it’s important to draw students’ attention to these phenomena. Subjects, like so many other features of language, are an aspect of the language that speakers already know about, that we have unconscious knowledge of. Figuring out the evidence for that is a useful exercise in scientific inquiry, and allowing students to “discover” the subjects that emerge beautifully when they make tag questions and perform SAI, reveals this knowledge.


A related lesson, which includes both Tag Questions and SAI, is here and a pdf of this lesson is here.

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