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Compound sentences are most often linked by a conjunction. These are words like, and, or, but, and yet.
My neighbor does not have a car. He doesn't want one. Two separate complete sentences
becomes
My neighbor does not have a car, and he doesn't want one. A compound sentencePlease turn on the air-conditioner. I will have a heart attack in this heat.
becomes
Please turn on the air-condoner, or I will have a heart attack in this heat.
Conjunctions link sentences by showing how ideas are related. Each conjunction shows a certain kind of connection between ideas.
Use of Comma:
Comma is used before the conjunctions in a compound sentence. If either part of the compound sentence does not express a complete thought, then don't use a comma before the conjunction
Examples:
"James brought flowers but forgot to give them to Helen." The second part of the first sentence has no subject, so no comma is needed
"James brought flowers, but he forgot to give them to Helen."
This statement has two complete sentences, so a comma is needed. The first example carries out the meaning better than the second by using the same subject only once in the first sentence because the same subject carries out the action in the second sentence, thus the comma is omitted in the second sentence. The second sentence uses the same subject as the first sentence, (James/he), which is unnecessary. Do not use the same subject in the second part of the sentence when the same subject carries out the action and don't use a comma.
Other Conjunctions:
There are pair conjunctions such as:
both ... and
either ... or
not only ... but also
neither ... nor
Examples:
Both I was promoted to a supervisory position, and I got a salary increase.
Either it rains when I go fishing, or it's sunny when I work.
Joining Ideas with a Semicolon:
Simple sentences can also be joined using a semicolon and a conjunctive adverb. A conjunctive adverb, is a word or phrase that works like a conjunction. As with conjunctions, it is important to choose the right conjunctive adverb.
Conjunctive Adverbs:
To show contrast: however, otherwise, nevertheless , on the other hand, in fact
to explain: for example, besides, further more
to show a result: as a result, therefore, thus
These words are used like conjunctions to join sentences. Place a semicolon (or comma) before the conjunctive adverb. You can use command after conjunctive adverbs.
Food prices keep rising; in fact, our weekly grocery bill is higher than last year.
Mark took tennis lessons; then she beat me all the time.
Semicolons Without Conjunctions:
Two simple sentences can also be joined without using a conjunction or a conjunctive adverb. A semicolon shows the ideas are linked.
Chen likes to barbecue; ribs are his specialty.
Summary:
You have learned that compound sentences can be formed in three ways:
1. using conjunctions and commas
2. using conjunctive adverbs and semicolons
3. using semicolons
Common Errors:
Run-on-Sentence: Common errors occur in forming compound sentences is caused by forgetting to use one of these methods. The result is is a a run-on sentence. In a run-on-sentence, Punctuation marks and conjunctions are either not used or misplaced.
Examples:
Incorrect: Mary needed new shoes, so she bought one pair. Correct: Mary needed new shoes so bought one pair.
Correct: Mary needed new shoes; consequently, she bought one pair.
Correct: Mary needed new shoes; she bought one pair.
Incorrect and repetitive use of ANDIncorrect: He went on vacation to New Mexico and visited Pueblo Villages and saw hot-air balloons and rode on a tram up the mountain.
Correct: He went on vacation to New Mexico and visited Pueblo Villages; he also saw hot-air balloons and rode on a tram up the mountain.
Comma Splice: This means the commas is used incorrectly to separate to sentences.Examples:
Incorrect: I keep sneezing, I think I'm catching a cold.
Correct: I keep sneezing, so I think I'm catching a cold.
Correct: I keep sneezing; I think I'm catching a cold.
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