When (if ever) is is acceptable to use an indefinite article immediately in front of an adjective? [duplicate]

Question

What's the rule for using a/an before an adjective?

I am asking this question because my high school professor is teaching us that we shouldn't use a/an before an adjective. With some 'exceptions' like "Picasso was a famous painter."

Now that sounds very strange to me because I am used to saying "It's a beautiful day.", not "It's beautiful day.", or "It's a small dog.", not "It's small dog". My professor also pointed out that "Picasso was a famous painter." was some kind of exception because "a" is used before an adjective. My professor also told me that this sentence is correct : "A mouse is an animal. It's small animal."

Like I said, for me, It's a very strange claim that we shouldn't use "a" or "an" before an adjective. What should I say to my professor? I would like your professional opinion about this.

Thanks.

Notice: This question isn't about 'a' vs 'an'. Read the question before marking it as a duplicate.

Answer 1

This is such a seemingly basic aspect of speech and writing in English that many guides don't even address it. But you may find this brief treatment of "The Adjective" in Warriner's English Grammar and Composition, Fifth Course (1977), a useful point of reference:

1c. An adjective is a word used to modify a noun or a pronoun.

To modify means "to describe or make more definite" the meaning of a word. The most frequently used adjectives are a, an, and the, which are called articles.

...

Usually an adjective precedes the noun it modifies. Sometimes for emphasis, a writer may place it after the noun.

EXAMPLE This land, so rich and flourishing, gave a new life to the immigrants.

I included Warriner's example here not because it illustrates the use of rich and flourishing as adjectives following the noun they modify (which was Warriner's primary purpose in presenting the example), but because it contains an instance in which a appears immediately before a simple adjective (new), in the phrase "a new life." This phrase presumably falls into the forbidden zone established by the supposed rule "Do not use a or an before an adjective."

I also like Warriner's observation that articles comprise a special (but very common) subgroup of adjectives, rather than belonging to an unrelated category of words.

Warriner doesn't make a big deal about phrases such as "a new life" because they are as common in English as cornstalks in Iowa. Everybody who speaks natural-sounding English uses them constantly—and I imagine that if you were to record a lecture by your professor, the recording would probably contain dozens of instances of the very same type of construction.