Technical writing can sometimes result in a long string of modifiers or adjectives before a noun. These are called noun phrases. Do you need commas?
Stainless steel electric submersible pump
No, you wouldn’t use commas here.
Long, black, flexible pipe
Yes, you need commas here.
Why the difference?
Noun phrases function as a single noun, and even if you put one adjective in front of it, it still does not need a comma.
Handmade white linen tablecloth = noun phrase
Expensive handmade white linen tablecloth = noun phrase with a single adjective in front of it, thus no comma. The word ‘expensive’ here is called a ‘superposed adjective,” one that modifies the whole noun phrase following it.
Here’s an excellent tip from the Yahoo Style Guide:
“If you have a string of adjectives and can’t decide whether they need to be separated by commas, try this trick: See how the sentence sounds with ‘and’ inserted between the adjectives. If inserting ‘and’ would result in an unnatural-sounding phrase, you are probably looking at superposed adjectives that don’t need commas. Consider the phrase ‘five beautiful antique wooden totem poles.’ Because you would not normally insert ‘and’ between any two of those adjectives, no comma in that phrase is desirable.
“Another clue is that you cannot switch the order of the adjectives in a series of superposed adjectives without violating English idiom: ‘Five antique wooden beautiful totem poles,’ for example, sounds quite odd. In the original phrase, each adjective, from five onward, is attached to the rest of the chain and should not be separated from it by a comma.”
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“One-Eyed, One-Horned Flying Purple People Eater”
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