Here are some key characteristics:
* It asserts something to be true. It makes a positive statement.
* It usually contains a subject and a verb. These are the essential elements of a sentence.
* It doesn't contain words like "no," "not," "never," or "don't." These words would make it a negative sentence.
Examples of affirmative sentences:
* The sun is shining.
* I love pizza.
* She is a doctor.
* They went to the park yesterday.
* We are going to the movies tonight.
Contrast with negative sentences:
* The sun is not shining.
* I don't love pizza.
* She isn't a doctor.
* They didn't go to the park yesterday.
* We aren't going to the movies tonight.
In essence, affirmative sentences declare something is true, while negative sentences declare something is false.