Use and or but to join two complete sentences to make a compound sentence.

Always use a comma before the joining word in a compound sentence.

Jiro-San knew many secrets of the sea. Taro learned some of them.

Jiro-San knew many secrets of the sea, and Taro learned some of them.

Jiro-San was Taro’s good friend. Yuko didn’t like him.

Jiro-San was Taro’s good friend, but Yuko didn’t like him.

Taro listened carefully from the rock. All he heard were seagulls crying.

Taro listened carefully from the rock, but all he heard were seagulls crying.

Together they cleaned the beach. Jiro-San’s old friends did not come.

Together they cleaned the beach, but Jiro-San’s old friends did not come.

One night they saw a school of dolphins. Another night they saw two whales swimming.

One night they saw a school of dolphins, and another night they saw two whales swimming.

The turtles laid their eggs on the beach. The eggs hatched eight weeks later.

The turtles laid their eggs on the beach, and the eggs hatched eight weeks later.