The dash, colon and semicolon are all punctuation marks that can be used to combine sentences. Using a dash or a set of dashes will offset an additional idea from the sentence to informally give more information. You can use a colon to illustrate an example of the idea stated in the sentence. A semicolon is used to connect clauses with related ideas.
Before: John wasn't having a good year. Four of John's pets died this year.
After: John wasn't having a good year: four of his pets had died.
Coordinating conjunctions are used to create compound sentences. And, but, or, for, yet and so are all coordinating conjunctions that are used in the simplest method of combining ideas. The coordinating conjunction in a sentence often follows a comma.
Before: Susan needs to do her homework. Susan is so tired that her eyes keep closing.
After: Susan needs to do her homework, but she is so tired that her eyes keep closing.
When two subjects are doing parallel actions in their sentences, you can combine the sentences.
Before: Matt ate dinner. Sarah ate dinner.
After: Matt and Sarah ate dinner.
When a subject is doing two actions, the sentences can be combined to describe both actions in one sentence.
Before: Matt ran down the hall. Matt jumped into bed.
After: Matt ran down the hall and jumped into bed.
If a subject is acting on the objects of two sentences in a parallel fashion, both actions can be included in one sentence.
Before: Matt needed to buy toothpaste. Matt also needed to buy a toothbrush.
After: Matt needed to buy toothpaste and a toothbrush.
Modifiers are words and phrases added to a sentence to describe nouns in the sentence. Modifiers can often be combined into one sentence.
Before: Samantha liked to read satirical novels. Samantha also liked to read historical novels.
After: Samantha liked to read satirical and historical novels.
Subordination is a way of combining sentences so that the idea of one sentence is made more important than the idea of the other sentence. When, although, if, who, what and that are all words that can also be used to subordinate one clause to another.
Before: Luke wanted to see a movie. They ended up playing mini-golf instead.
After: Although Luke wanted to see a movie, they ended up playing mini-golf instead.
Appositives can be used to describe something previously mentioned in a new way. This new word or phrase is placed parallel to the subject or object in the sentence.
Before: Aaron was the best athlete in the school. Aaron won the tennis match.
After: Aaron, the best athlete in the school, won the tennis match.
Participial phrases can be used to place the idea of one sentence in the structure of another sentence by changing it into a modifying phrase.
Before: Aaron worked long hours all summer. He managed to save up enough money to buy a car.
After: Working long hours all summer, Aaron managed to save up enough money to buy a car.