Simplify the following text for a Grade 6 native English-speaking person.
Original: A run-on sentence is two or more sentences , put together into one sentence , without anything to join them together .
Simplified: The mere fact that a sentence is long does not make it a run-on sentence ; sentences are run-ons only when they contain more than one complete idea . A run-on sentence can be as short as four wordsâ '' for instance : I drive she walks .