An independent clause without a subordinate is sentence fragment?

That's correct! An independent clause without a subordinate clause is a sentence fragment.

Here's why:

* Independent clause: A group of words that contains a subject and a verb and expresses a complete thought.

* Subordinate clause: A group of words that contains a subject and a verb but does not express a complete thought on its own. It needs to be connected to an independent clause to make sense.

Examples:

* Sentence fragment: The cat on the mat. (No verb)

* Sentence fragment: Running through the park. (No subject)

* Sentence fragment: Because she was happy. (Subordinate clause only, needs an independent clause)

* Complete sentence: The cat on the mat sat and watched. (Independent clause)

* Complete sentence: She was happy because she got a new toy. (Independent clause + subordinate clause)

In summary: An independent clause on its own is a complete sentence, while a subordinate clause needs an independent clause to make a complete thought.