This is a simple decision tree to help you decide which article to use. By answering a series of questions, you can find out which article to use with a particular noun.
Please note that this system is very basic. It only deals with the, a/an, and the zero article (nothing), and there are many exceptions to the “rules” shown here.
Question: Is the noun definite or indefinite?Do both the reader and writer (or the listener and speaker) know WHAT the noun refers to? For example, has it been mentioned before in the text or the conversation?
Answer: Use “the” (the definite article).
Question: is the noun count or non-count?Does the noun refer to something you can count (e.g. “book” — one book, two books, three books), or something you cannot count (e.g. “water”)?
Question: is the noun singular or plural?
Answer: Use NOTHING (the Zero article).
Question: Does the noun begin with a vowel or a consonant?Does the noun begin with A, E, I, O or U (the vowels), or one of the other letters (the consonants)?
Question: Is the first letter a U?
Question: Does the beginning of the word sound like “Y-”?Some words beginning with U have a Y- sound at the beginning (for example “university” or “unique”). Others (such as “unhelpful” or “upset”) don't.
Answer: use “an”.
Answer: use “a”.