How do you find the subject of a sentence?

The subject is “what the sentence is about.”

If the sentence is in the active voice, then the subject of the sentence is the “doer” of the action described by the main verb.

For instance, in the sentence “Kate has to write her aunt a thank-you letter,” “Kate” is the subject (she is “doing” the writing).

If the sentence is in the passive voice, the subject is not the doer, it is the “recipient” of the action (or occasionally the thing being “transferred”).

For instance, if the information from the example above is expressed in the passive voice as “Kate’s aunt has to be written a thank-you letter,” the subject is “Kate’s aunt” (the recipient).

In the sentence “A thank-you letter has to be written to Kate’s aunt,” which is also in the passive voice, the subject is “a thank-you letter” (the thing being transferred).

Have you tried QuillBot’s free Grammar Checker? You can use it to check that the verbs in your sentences “agree with” the subjects.