Chapter I. The article 1 the definite and indefinite article

What are Indefinite Articles?

“A” and “An” are the indefinite articles used before a noun that has an unspecified identity. They are used to refer to a general idea rather than
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one particular thing.
Example
Publishing a book is the lifetime goal of my father.
“A book” refers to an unspecified book that the author’s father is willing to have published one day.
Example
An external influence includes unavoidable factors a business may encounter.
“An external influence” does not refer to a specific external influence, but rather to any external influence in general.
Example
In this research paper, an irregularity of a composite was studied. The irregularity found during the experiment proved the hypothesis.
“An” is used when “irregularity” is first mentioned and “the” precedes the irregularity mentioned the second time.

When to use indefinite articles

Type of Noun	When to Use	Example
Countable noun	One member of a countable noun	I have an idea for our research paper.
	First mention of a countable noun	We found a concept.The concept was inspired by a work of art.
Uncountable noun	Never used with indefinite article	N/A

Using articles before singular nouns

A singular countable noun always requires an article before it while a plural noun does not always require an article. The same rule applies for using “the”, “a” or “an”, depending on whether a noun is specific or unspecific. When/how to use the indefinite article depends on the sound of how the word begins. “A” comes before the words that begin with a consonant sound while “An” precedes words that begin with a vowel sound.
Example
Our team came up with an idea of recruiting the participants of the experiment among the psychology students. The idea was to gather information from people actually studying the relevant area
Here, “idea” is a singular countable noun. Writing “an idea” indicates that this idea has not been introduced yet. The use of “the idea” in the following sentence indicates the idea from the previous sentence.