C4 Don’t join two sentences with merely a comma (or worse, with no punctuation at all).
Here are six ways to correct this problem:
Solutions	Incorrect Examples	Correct Examples
Solution A: Make a compound sentence by using a comma and a conjunction.	He tried to climb the fence, it was just too hard.	He tried to climb the fence, but it was just too hard.
Solution B: Separate the halves into two complete sentences.	He tried to climb the fence, it was just too hard.	He tried to climb the fence.  It was just too hard.
Solution C: If the halves are similar, make a compound sentence with just a semicolon.  (Don’t use a conjunction with a semicolon.)	When he was young, he fell for everything, when he was old, he trusted nothing.  He loved the little dog, she loathed the wretched thing.	When he was young, he fell for everything; when he was old, he trusted nothing.  He loved the little dog; she loathed the wretched thing.
Solution D: A writer may use a long dash to join a long appositive to the end of a sentence.	She had had a narrow escape, it was an experience she would never forget.  He stepped back and observed the result, it was a thing of beauty.	She had had a narrow escape – an experience she would never forget.  He stepped back and observed the result – a thing of beauty.
Solution E: If a complete sentence introduces a list, a writer may use a colon (:).	When I saw this boat I thought of two things, first, that there was a way off this accursed island, but second, that I was no longer alone.	When I saw this boat I thought of two things: first, that there was a way off this accursed island, but second, that I was no longer alone.
Solution F: Change the wording to make one of the halves depend on the other one.	I squeezed myself behind the plywood, I could hear the breath of the killer searching for me.	I squeezed myself behind the plywood, listening closely to the breath of the killer searching for me.