We learned that a comma goes between items in a list. Mom bought eggs, milk, and bread.
We also sometimes put a comma in a list of two adjectives.
Calculus is a challenging, difficult math course.
Challenging and difficult are both adjectives that describe the math course. Calculus is challenging. Calculus is difficult.
We use a comma between two adjectives when and between the two adjectives makes sense.
Calculus is a challenging and difficult math course.
Calculus is a challenging, difficult math course.
We also use a comma between two adjectives when the adjectives make sense in either order.
Calculus is a challenging, difficult math course.
Calculus is a difficult, challenging math course.
Sometimes two adjectives describing the same noun do not get a comma in between.
Jan lives in the small brick house.
The house is a small house.
The house is a brick house.
But we cannot put and between the two adjectives. Jan lives in the small and brick house makes no sense.
We cannot change the order of the two adjectives. Jan lives in the brick, small house makes no sense.
Therefore, we do not put commas between the two adjectives in this sentence.
We put a comma between two adjectives when the two adjectives make sense using and in between them.
We also put a comma between two adjectives when changing the order of the adjectives does not change the meaning of the sentence.