Here's why:
* It joins two independent clauses. An independent clause can stand alone as a complete sentence.
* It shows a contrast or difference between the two clauses.
For example:
"I love pizza, however, I'm trying to eat healthier."
Here, "I love pizza" and "I'm trying to eat healthier" are both independent clauses, and "however" connects them, showing that the two statements are contrasting.
While sometimes used to start a sentence, it is important to note that "however" is grammatically correct when used internally in a sentence and is often preceded by a semicolon.