* Complex sentences require a conjunction: A complex sentence has an independent clause (a complete thought) and a dependent clause (a thought that relies on the independent clause). These clauses are joined by a conjunction like "because," "although," "since," "while," etc.
* Conjunctions are often followed by commas: To separate the independent and dependent clauses, a comma is typically placed before the conjunction.
Example:
* Without punctuation: The dog barked the cat ran away
* With punctuation: The dog barked, and the cat ran away.
Therefore, even if you try to omit other punctuation, you'll still need a comma to separate the clauses in a complex sentence.
You can write a complex sentence with minimal punctuation, but a comma is essential for clarity.