When two or more adjectives come before a noun, sometimes a comma goes between them and sometimes not. Coordinate adjectives each describe the noun on their own, like items in a series: “a long, cold winter.” Cumulative adjectives build on each other in a set order: “a big red barn.”
Key idea
Two tests: switch the order, or put and between them. If both still sound natural, the adjectives are coordinate: use a comma. If not, they are cumulative: no comma.
Why it works
The comma stands for the and you could say: “a long and cold winter.” In a cumulative pair, the first adjective describes the whole phrase after it: in “a big red barn,” big describes the red barn. English puts such adjectives in a usual order (number, opinion, size, age, color, material), which is why switching them sounds wrong.
Worked example: Coordinate
“a bright cheerful kitchen”
- Switch: “a cheerful bright kitchen.” Sounds fine.
- Add and: “a bright and cheerful kitchen.” Sounds fine.
- Both tests pass, so use a comma.
Answer: a bright, cheerful kitchen
Worked example: Cumulative
“a shiny new bike”
- Switch: “a new shiny bike.” Possible, but it changes the stress.
- Add and: “a shiny and new bike.” Odd.
- The and test fails, so no comma.
Answer: a shiny new bike
Common mistake
Putting a comma between every pair of adjectives, or after the last one: “a long, cold, winter.” Never put a comma between the last adjective and its noun.