Definite vs. Indefinite Articles: An Important Distinction

Did you know that the severed head of a sea slug can grow a whole new body? An interesting fact, huh? How about this fact: Those first two sentences use all three primary definite (the) and indefinite articles (a, an).

Articles, a type of subtle adjective always placed before a noun, so commonplace you might not even notice them, play the critical roles of clarifying a noun’s known or unknown identity and quantifiable or unquantifiable amount. 

Although small, articles communicate a lot about nouns. A misused or forgotten article can critically alter your reader’s understanding of what your nouns are, how many there are, and how well you know them. There are two categories of articles, definite and indefinite, whose usage depends on the noun that follows them:

Definite article 

• The (before a singular, plural, or uncountable noun, defined identity)

Indefinite article

• A (before a countable, singular noun, with undefined identity, that starts with a consonant)
• An (before a countable, singular noun, with undefined identity, that starts with a vowel)

No article

• Use no article before uncountable nouns with undefined identity.

Factors Determining the Usage of Articles

Remember, a noun’s status determines which article you use, and its status depends on three factors:

• Is the noun countable or uncountable?
• Is the noun’s identity definite (defined, known) or indefinite (undefined, unknown)?
• Does the noun (or the added adjective before it) start with a vowel or consonant?

Factor #1: Countable (the, a, an) vs uncountable (the or no article) nouns

Countable nouns, of which you can count the exact number, are measured in number rather than amount. For example, looking at a grass field, I can count the number of blades of grass in the field. I can count one blade of grass, two blades of grass, and so on. Therefore, blades of grass is a countable noun, and I would use the, a, or an as an article for it, depending on if it started with a vowel or consonant, and if its identity is particularly indicated.

• Correct: A blade of grass (countable, consonant, undefined)
• Correct: The blade of grass (countable, consonant, defined)
• Correct: An ugly blade of grass (countable, vowel, undefined)
• Incorrect: Look at a grass.

As a general rule of thumb, if you can add a letter s at the end of the noun to pluralize it, it’s a countable noun.

Countable noun examples (which use the, a, an): Blades of grass, grains of sand, people/persons in a crowd, drops of water, apples in a tree

Conversely, uncountable nouns, which don’t have a specific number, are instead counted by amount. If I switch from blades of grass to just talking about the grass in the field, I cannot count one grass, two grass, and so on. Instead of the number, I refer to the amount of grass. Uncountable nouns use the article the if their identity is defined or specified, and no article at all if their identity is undefined or unspecified.

• Correct: Look at the grass. (uncountable, defined identity)
• Correct: Let’s go look at grass. (uncountable, undefined identity)
• Incorrect: Look at a grass.

Uncountable noun examples: Some substances like sand, air, grass, clothing, water; most abstract ideas like happiness, anger, love; food and drink items like Coca-Cola, spinach, coffee

Factor #2: Identity known/definite (the) vs. unknown/indefinite (a, an, or no article)

I know the goal, but I need to find a path to get there.

If the speaker knows the exact subject or object that they reference, that noun has a known identity. For example, if I say the books on my desk or even the book pile on my desk, I speak about a specific book or set of books. The article the is considered a definite article because it refers to a defined, or known, noun.

Definite nouns use the article the, regardless of singular or plural status, and regardless of vowel or consonant letters.

• Correct: Please buy the bed from the store. (specifically defined bed, singular)
• Correct: Please buy the organic apples from the store. (specifically defined apples, plural)

On the contrary, if I say a book on my desk, or an open book, I no longer speak of a specific book or set – the noun now has an unknown exact identity, a general idea or category from which to pick. The articles a and an refer to indefinite, or undefined, nouns. Use the article a if the noun starts with a consonant, and the article an if the noun begins with a vowel.

• Correct: I want a dog. (consonant, undefined dog)
• Correct: I want an Australian shepherd. (vowel, undefined dog)

Factor #3: Nouns that begin with a vowel vs. a consonant

Would you rather have an egg or a piece of bacon for breakfast? 

While a tough breakfast choice, the article choice becomes straightforward when you remember that you use the indefinite article a to precede consonant-beginning nouns, and an to precede vowel-beginning nouns. 

Keep in mind that this distinction only applies to the articles a and an, which we only use for singular, countable objects with an indefinite (unknown) identity.

• Correct: Please buy me an apple.
• Incorrect: Please buy me a apple.
• Correct: Please buy me a cantaloupe.
• Incorrect: Please buy me an cantaloupe.

If a noun has an adjective in front of it, the initial letter of that adjective becomes the first letter of the new noun phrase, and you must adjust your article accordingly.

• Correct: My girlfriend brought me a tasty orange.
• Correct: My girlfriend brought me an orange.
• Incorrect: My girlfriend brought me a orange.
• Incorrect: My girlfriend brought me an tasty orange. 

Final note: Some, all objects, or objects in general

I don’t know why they do, but slow walkers bother me. Not some, all slow walkers.

The above statement, while perhaps unjustified, demonstrates the correct approach to referring to some objects of a category, all objects of a category, or a category of objects in general. 

When referring to a limited amount of a countable or uncountable item, use the indefinite article some.

• Correct: Please bring me some soup.
• Correct: Please bring me some sandwiches.

Use no article when referring to all of a group or a group in general, regardless of the countability, instead just stating the group.

• Correct: I love to watch birds.
• Correct: I enjoy movies.

As you work through your next piece of writing, keep in mind the three rules of indefinite vs. definite articles, and your language will maintain a valuable clarity.