When to Use "a":
* Singular, countable nouns: "a" is used before singular nouns that you can count.
* Example: "I saw a dog in the park." (One dog)
* Nouns starting with a consonant sound: This is the most common rule.
* Example: "a cat", "a house", "a university"
* Nouns starting with a vowel sound, but spelled with a consonant: This is a tricky one.
* Example: "a European", "a one-way ticket"
* "A" can be used with some numbers:
* Example: "a dozen eggs", "a hundred people"
When to Use "an":
* Singular, countable nouns starting with a vowel sound:
* Example: "an apple", "an hour", "an umbrella"
* Singular, countable nouns starting with a silent "h":
* Example: "an honor", "an hour"
When to Use No Article:
* Plural nouns:
* Example: "I saw dogs in the park."
* Uncountable nouns:
* Example: "I like water."
* Proper nouns:
* Example: "I live in London."
* Abstract nouns:
* Example: "Love is a powerful emotion."
Important Note: The use of articles is a complex topic in English. These are just general guidelines. There are exceptions and nuances, and it's always best to consult a grammar guide or dictionary when in doubt.