Have you ever noticed that sometimes you use commas in a list of modifiers, and sometimes you don’t?
“The big black car turned the corner.”
“The shiny, bright car turned the corner.”
So why is that?
Because adjectives have an order.
(Silence fills the room)
You have different types of adjectives: quantity, quality, size, age, color, origin, and type. The website http://grammar.ccc.commnet.edu/grammar/adjectives.htm actually breaks it down further in a table called “The Royal Order of Adjectives”: Determiner (four, her), Observation (shiny), Physical Description (size, shape, age, color), Origin (English, French), Material (silk, metal), Qualifier (basketball). But I can’t remember that much, so I’ll go with the first list.
When you have two adjectives in a list, if they are of different types–color and quality, like the first example–then you don’t need a comma (big black car). If you have two of the same type, like two quality adjectives (shiny, bright car), then you need a comma. Think of it this way–if a sentence would sound right if you add an “and,” you would need a comma: “The shiny and bright car.” (It actually sounds childish to say “the shiny bright car.”) But you wouldn’t say “the big and black car.” No comma. It’s even more noticeable with numbers and qualifiers. You certainly wouldn’t say “the two and green shirts” or “the old and English purse.”
And … you should line your adjectives up in that order. It’s just weird to say “black two cars.” No, you would say “two black cars.” And in a long list, you don’t have a comma between the first two of different classes, or the last two, but between all the middle ones. So, “the four expensive, gigantic, old, green, English silk purses.”
Never thought there was a science to it, did you? Me neither. Sometimes our language exhausts me.