To write well, you need to know how to punctuate your sentences.
Commas and full-stops (periods) are most often used.
You use commas to separate compound sentences. A compound sentence is made up of 2 or more simple sentences. First of all, a simple sentence has a subject, a verb, and or an object.
e.g. He laughed. (simple sentence: subject + verb)
e.g. He laughed at me. (simple sentence: subject + verb + object)
e.g. He left the room. (simple sentence: subject + verb + object)
e.g. I was all by myself. (simple sentence: subject + verb+ complement)
However, you cannot join two or more simple sentences together without a coordinating conjunction (and, but, or, nor, for, so, yet)
e.g. He laughed at me, he left the room. (incorrect: there is no coordinating conjunction)
e.g. He laughed at me, and (he) left the room.(correct)
e.g. After he laughed at me, he left the room.(correct: "he laughed at me" becomes a subordinate clause and no longer a simple sentence with the addition of the subordinating conjunction "after")
e.g. He laughed at me, left the room, and I was all by myself. (correct)
You may or may not need a comma for a compound or complex sentence. A complex sentence is made up of a simple sentence and one or more subordinate clauses (a subordinate clause is an incomplete sentence joined to a simple sentence by a subordinating conjunction, such as after, when, since etc.
e.g. He saw me and he shook my hands. (a compound sentence joining 2 simple sentences by a coordinating conjunction: "and": " he saw me" and "he shook my hands")
A comma before and is optional. If you think the sentence is too long or the meaning is misleading, you may want to add a comma.
By the same token, if you think the complex sentence is too long, then you may want to add a comma.
e.g. When he saw me walking with the Mayor along the corridor, he shook my hands.
e.g. He shook my hands when he saw me. (without the comma)
I hope you have learned the following: a simple sentence, a compound sentence, a coordinating clause, a subordinating clause, and the use of comma.
Copyright© by Stephen Lau