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Lesson 2.2 Clauses and Subjects: Subject-Auxiliary Inversion (SAI)

downloadable subjects and SAI worksheet


In Lesson 2.1, we saw one test (tag questions) for identifying the subject of a clause. Being able to easily pick out the subjects of our sentences will help ensure

  • that each sentence has a subject

  • that the subject “agrees with” the verb

  • that each independent clause has only one main subject


We make use of subjects all of the time in our speech, and have no problem doing so. Here’s some cool evidence for that knowledge.


When a speaker of English turns a statement into a question, the subject changes places with the auxiliary (or helping) verb.


These auxiliary verbs include forms of have and be, as well as the modal verbs: can, could, shall, should, will, would, may, might, and must.


            The chicken will eat the corn.         becomes           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.            becomes            Is Mo eating carrots?


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


Activity: Turn the following sentences into questions by using SAI. Underline the subject that is revealed when you do this.


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.


[Teacher Notes:  Subject Auxiliary Inversion (SAI) will always pick out the subject of an independent clause, not a subordinate (also called dependent) clause, so it will distinguish these from each other. Distinguishing subordinate clauses from independent clauses is an important aspect of learning not to write in fragments, since one of the most common types of stigmatized fragments in writing is a subordinate clause. Consider, for example, the following complex sentence.


            The monkey can see that the banana is ripening.


This sentence contains two clauses: the independent clause and the subordinate clause, that the banana is ripe, contained within it. Apply SAI, and you get


            Can the monkey __ see that the banana is ripening?


Employing SAI picks out the independent clause subject, the monkey. Even though the banana is also a subject (of the subordinate clause), SAI will not work with that subject since the banana is not the subject of the independent clause.


            *The monkey can see that is the banana __ ripening?         


SAI is, therefore, a useful test to determine whether a sentence has the subject that is required in most forms of formal writing. When SAI is attempted with a sentence without an independent clause subject, the result is ungrammatical.


            Because he does not like it.       becomes    *Because does he not like it?


SAI fails here since because introduces a subordinate clause and there is no independent clause subject. Similarly for other kinds of fragments, SAI will not work since there is no subject.


            At the skateboard store.    becomes    ??           


There is no auxiliary verb and there is no way to turn this into a question.]


key words: subjects, auxiliary verbs, fragments, run-ons, clause types, complex sentences


CCSS.ELA-Literacy.L.3.1i Produce simple, compound, and complex sentences. 

CCSS.ELA-Literacy.L.4.1c Use modal auxiliaries (e.g., can, may, must) to convey various conditions. 

CCSS.ELA-Literacy.L.4.3c Differentiate between contexts that call for formal English (e.g., presenting ideas) and situations where informal discourse is appropriate (e.g., small-group discussion). 


Here is this lesson as a pdf.


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