fragment / complete sentence

A piece that cannot stand alone versus a sentence that can.

A complete sentence is an independent clause: it has a subject and a finite verb, and it can stand alone: The lock jammed. A fragment cannot stand alone. It may lack a subject or a finite verb (After the storm. Running late.), or it may have both but remain a subordinate clause (When the lock jammed. Because the lock jammed.). Attach the fragment to an independent clause, or rewrite it as one.

Examples

Use The pump failed. (Independent clause.)

Use When the pump failed, the line stopped. (Subordinate clause attached.)

Avoid When the pump failed. (Subordinate clause alone.)

Avoid Running late. (No finite verb.)