The Basics of Article Usage in English: "A," "An," and "The"

Using articles (a, an, the) is one of the trickiest aspects of writing in English. This difficulty is not surprising, as different languages have different rules for article usage (assuming they even have articles), and the rules in English can seem confusing even to native English speakers! However, using articles correctly is one important way to make your writing sound natural. With this in mind, here are a few helpful guidelines that will help you decide when an article is needed (and which one to use) and also when one is not needed. See the flowchart at the end for a handy reference.

'The' versus 'A' / 'An'

A good rule of thumb to use is to ask whether the noun that is being modified is the only one of its kind or if it exists in more than one form/case. If it is the only one of its kind or you are referring to only one specific example, use 'the':

• The assay was conducted to identify the organism responsible for the outbreak. (This sentence refers to a specific assay, organism, and outbreak.)
• Note: Articles are frequently missing from titles, section headings, and figure legends. ("The effect of different culture temperatures on bacterial growth kinetics" and "The characterization of a new ginsenoside compound" both should include 'the' because specific results are being discussed.)

However, if the noun you are modifying is one of many (e.g., an example or a single member of a group), you should use 'a' or 'an':

• A standard genome sequencing protocol was used to identify an exciting new species of Escherichia. (The protocol used was one of several available sequencing protocols, and other Escherichia species had already been identified.)

Other times to use 'the' (and times NOT to use it)

If you are referring to a noun as a representative of every instance/individual (i.e., a general discussion), it can be appropriate to use 'the' with the singular form of the noun. 'The' is used primarily in scholarly writing when referring to machines, animals, and bodily organs.

• The smartphone has made it easier for employees to work from home.
• The dolphin is considered one of the smartest animals.
• The lung contains over 300 million alveoli.
• Note: It is most common to use the plural form of the noun in cases such as these, but remember to omit the article. (Smartphones have made it easier for employees to work from home. Dolphins are considered some of the smartest animals. Lungs contain over 300 million alveoli.)

Not every noun requires an article when used in this general way, though. Mass nouns (or non-count nouns), which refer to abstract or uncountable things, do not need an article:

• Temperature can be expressed in Fahrenheit, Celsius, or Kelvin.
• Knowledge is the key to happiness. (But: "The knowledge that she was receiving an award made her happy" requires an article because a specific understanding is referred to.)

Most proper nouns (such as the names of countries or people) also do not require an article:

• Tesla was one of the greatest inventors of all time.
• The samples were collected in Hebei Province.
• Collective proper nouns are an exception: the Middle East and the Great Lakes
• When a person's name is part of a theory, test, etc., it may sound more natural to use 'the' (e.g., the Doppler effect or the Riemann hypothesis). However, you should not use 'the' if the name is possessive (e.g., Tukey's test, Riemann's hypothesis).

'A' versus 'An'

'A' is used before words that start with consonant sounds ("a sample" or "a model"), even if the consonant sound is made by a vowel ("a unit"). Conversely, 'an' is used before words that start with vowel sounds ("an equation" or "an element"), even if the word starts with a silent consonant ("an hour").

We hope that this tip has been helpful! Of course, the best way to become more familiar with using articles is to read a lot, especially papers close to your research topic, which will give you a better feel for how articles are used in your field. Please also feel free to contact us with any questions.

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