Run-On Sentences are basically two full sentences that could function separately, but have been incorrectly combined into one.
Incorrect Example: I love summer, I hate winter because I hate the cold.
This is a run-on because both ideas are independent, and pushing them together makes the sentence confusing and wordy.
You can fix run-ons by separating the two ideas with a period. Use a semicolon if the two ideas are related:
Correct Example: I love summer; I hate winter because I hate the cold.
You may also separate them with a comma and a conjunction such as “and” or “but”:
Correct Example: I love summer, but I hate winter because I hate the cold.
We would use the conjugation "and" when the the second clause of a sentence confirms the initial one. The use of "and" underscores similarity between the clauses:
Correct Example: I love summer and I enjoy going to the beach.
Incorrect Example: He was an excellent athlete back in high school and he has gained some weight since.
We use the conjugation "but" when the second clause of a sentence partially negates the initial one. In other words, the use of "but" links two clauses that contrast one another:
Correct Example: He was an excellent athlete back in high school but he has gained some weight since.
Incorrect Example: I love summer but I enjoy going to the beach.