A grammatical fragment is when a dependent clause is separated from the main sentence. This usually occurs when you put a period in the middle of what should be once sentence.

(Example: I need to find a new roommate. Because the one I have now isn’t working out too well.

Should be: I need to find a new roommate, because the one…..)

Fragmented sentences: Fragmented sentences occur when a sentence lacks either a subject or verb or when a sentence is actually a phrase masquerading as a sentence. Fragmented sentences are always incomplete thoughts. For example “Near the printer on my desk” has neither a subject nor a verb. “Twenty seven females and ten males” has no verb and “Went willingly to the room” has no subject. All necessary parts of speech must be within a particular sentence. So “The stapler sits near the printer on my desk” adds a subject (i.e., stapler) and verb (i.e., sits). “Twenty seven females and ten males participated in the study” adds a verb (i.e., participated). “She went willingly into the room” adds a subject (i.e., She). Sometimes a fragmented sentence does have an action and an actor, as in “Bill, running down the corridor.” The problem here is that the thought is incomplete. “Bill ran down the corridor” is a complete thought, as is, “Bill, running down the corridor, smashed head first into Dean

A sentence fragment is simply incomplete. It doesn’t have a subject and verb, (and isn’t an imperative) or is otherwise incomplete. (For eg you can’t use the “ing” form of the verb alone; it requires an auxiliary.