In English, adjectives do not take a plural form. How do we explain the use of the adjective "sales" (as in sales growth, or sales decline)?
According to Lexico, sale is not an adjective.
You are confusing a category of words adjectives with a function in noun phrase structure modifier. Modifiers in NPs can come from a variety of different categories. A selection from CaGEL p444:
i a. another three days b. the barely forty students present [Determiner Phrase]
ii a. his wry attitude b. many very angry farmers [Adjective Phrase]
iii a. the defeated army b. her recently published article [Verb Phrase]
iv a. the gleaming showroom b. three steadily melting marshmallows [Verb Phrase]
v a. its entertainment value b. those Egyptian cotton shirts [nominal]
vi a. a dogs’ home b. a young children’s edition [nominal]
Sales, as it is used in sales growth, is a mass noun (Lexico):
1 [mass noun] The exchange of a commodity for money; the action of selling something.
‘we withdrew it from sale’
1.1 (sales) A quantity or amount sold.
‘price cuts failed to boost sales’
1.2 (sales) The activity or business of selling products.
‘director of sales and marketing’
Sales is a plural noun.
[Noun1][noun2] = the [noun2] associated with [noun1]
The Language Department = the department associated with language.
A beer bottle = a bottle associated with beer.
There can be several nouns together:
A beer bottle shape = a shape associated with a bottle that is itself associated with beer.
Thus "sales growth" = the growth associated with sales.
The nature of the association is given by the context.
Although people often use the words "never" and "always" to describe rules about the English language reality is often more of "not usually" or "usually."
Imagine a wooden barrel full of apples, where each apple has either a red or green skin. Someone named "Irene" might say, "all of the apples in the barrel are red." Well, if you find a green apple, IRenestatement suddenly is put to the test. A truer statement is, "more than 90% of the apples in the barrel are red."
I encourage to translate any of the following statements...
- "In English, we never [...]" - "In English, we always [...]" - "English has no [
- "More than 90% of the time, [...]"
- "More than 90% of the time, [...]"
- "English has almost no [
You might view the rule "In English, adjectives never take on a plural form," more like "adjectives usually aren't plural."
In the case of "sales growth" or "sales decline" the word "sales" is an adjective.
"Johann studies tree growth" More than 90% of the time tree is usually a noun, but in this case, tree is an adjective.
Hannah studies baseball statistics
baseball is usually used as a noun. But, in this example, baseball is being used as an adjective.
- Ian specializes in home design. (What kind of design? home design)
- Jacob likes flower arranging. (What kind of arranging? flower arranging)
Aaron works as a dog trainer
In the example, "dog" is being used as an adjective acting on the word "trainer"
However, dog is usually a noun.
Pretty much any noun in English can be turned into an adjective.
Usually, a flat-bladed screwdriver is used put loosen or tighten single-slotted screws. However, flat-bladed screwdriver can also be used as a small pry bar. Words are tools, like screw-drivers. The word "Sales" is a tool.
The words "Sales" is sometimes used as an uncountable noun.
Notice that is it is awkward (not incorrect, but rare) to write things like:
- two golds, three golds, four golds
- one water, two waters, three waters
"Sales" is sometimes used as a countable noun...
- 1 sale - 2 sales - 3 sales, 4 sales...
Other times, "Sales" is used as an uncountable noun:
- sales are up
- sales are down
- we need to increase sales
In the phrase, "sales growth," the word "sales" is an adjectivized uncountable noun.