That scary, eager young teacher with the bright red pencil and the old-fashioned, rather smelly sweater - she might have taught you grammar but probably never taught you how to tell whether you need a comma between multiple adjectives such as scary, eager, young, bright, red, old-fashioned, and rather smelly.
Adjectives, when they come in twos and threes or more, are either cumulative or coordinate. Either they pile up in front of the noun, accumulating there, adding one meaning to another in a very particular order, or coordinate - are of equal importance. One kind gets a comma between them, one doesn't. But which is which?
Try a few tests before lapsing into a comma, as Bill Walsh of the Washington Post puts it in his very dry and funny style guide,
Here are some other examples:
thin white line
shiny black Cadillac
large, open spaces.
What should you do?
The easiest test: See if you can put an "and" in place of the comma and still have the phrase make sense. If you can say the "little and old lady," add a comma. (To put it another way, are you trying to say that the old lady is little or that the lady is little and old?) If that sounds just so wrong, you can't. If you can say "the old-fashioned and rather smelly sweater" and "the scary and eager teacher," use the comma.
A second test is to see if you can add an "and" and switch the order: "the young and scary teacher," "the rather smelly and old-fashioned sweater." (Again, is the scary teacher young, or is the teacher young and scary?)
There are other ways, but these are possibly the quickest and most useful.
Remember, in adjectives before a noun, switch out the commas for "and"s and see how it works. Comma = "and" in adjective series.
