Is this a sentence fragment?
Two sentence twists will tell you

A sentence fragment in spoken language often conveys a complete thought to hearers. Spoken language has ways of compensating for missing fragments of a sentence. By contrast, written language does a poor job of suggesting the missing sentence bits.

Experienced writers sometimes write an incomplete sentence on purpose, to create a specific effect.

Novice writers are more likely to write an incomplete sentence by accident because they aren't totally in control of their writing. They put traditional sentence boundaries (a capital letter at the left and a period at the right) around non-sentences without being aware they are messing up.

The answer is not drill on sentence parts or more worksheets.

Students need to learn how to take something from their own writing that has traditional sentence boundaries and check it for completeness.

Check wholeness with tag and Y/N

Writers can learn to spot and repair a sentence fragment using Rei Noguchi's method of isolating grammatical subjects.

Noguchi uses a simple two-part strategy for identifying the subject in a declarative sentence. He creates both a tag question and a yes-no question based on the original sentence.

It is impossible to form either a sensible tag question or a sensible yes-no question from a sentence fragment.

Let me show you.

Tag and Y/N from whole sentence

First, look at this example that uses a complete sentence.

Original sentence: If it does not rain tomorrow, he will go.

Tag question: If it does not rain tomorrow, he will go, won't he?

Yes-no question: Won't he go tomorrow if it does not rain?

Each of those sentences makes sense.

Tag and Y/N from sentence fragment

Compare that to this:

Original. If it does not rain tomorrow.

Tag question: If it does not rain tomorrow, does it?
Yes-no question: Does it rain tomorrow if?

Sensible tag and yes-no questions cannot be created from the fragment.

Fragment fixes

Often when students force fragments into the tag and yes-no formats, they add words. What students add suggests what the fragment needs in order to become a complete sentence. For example,

Original: Just hanging out.

Tag question: Just hanging out, are they?

Yes-no question: Are they just hanging out?

To make both the tag and the yes-no question, students must add a subject. That's a dead giveaway that the original lacks a subject.

If students put a subject with the original like this

They just hanging out.

most will hear that the sentence fragment needs a helping verb. Students who don't "hear" that missing verb helper need some formal grammar study (written and oral) to develop more upscale grammar.

Want to borrow Noguchi's book?

Want to borrow a copy of Noguchi's book Grammar and the Teaching of Writing: Limits and Possibilities,? Use the WorldCat search box to find libraries around the world that have it.

If you live near a public college or university, you may qualify for a community borrower's library card. The nice folks at the State University College at Oneonta even helped me get a parking permit for the year. Many private institutions have similar community borrower privileges. It doesn't hurt to ask; that's how I got borrowers' privileges at Hartwick College.