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A – specific / A–unspecific

One in particular / Any one as an example

Hale-Bopp comet


One in particular / Any one as an example


Use "a" to refer to one you observe or have knowledge about.

A comet was seen in the western sky last night. (first mention)

The comet was believed to be Hale-Bopp.

The comet has a spectacular, bright tail.



Use "a" to talk about one in general (one as an example of all; true of all comets).

A comet appears to have a tail as it streaks through the sky.

A comet also has a dense head.

If you look up in the sky, you might see a comet.


Astronomy and Space Resource





Practice 1

A Particular One or Any One?

a black hole



Any one or a particular one?

  1. Select your response.
  2. Compare your response to the feedback by clicking the "check" button.


A black hole is an object, typically a collapsed star whose gravity is so strong that its escape velocity exceeds the speed of light. Since nothing is known to exceed the speed of light, nothing can escape from a black hole.

A black hole

A planet was later discovered farther out in the solar system. The planet, Jupiter, named after the Roman god, was the largest of all.

A planet








Practice 2

Any One or a Particular One ?

a comet



A particular one (specific) or any one (unspecific)?

  1. Select the response from the list that best completes the sentence. 
  2. Compare your response to the feedback by clicking the "check" button.


People did not always know what a comet was. In ancient times, people thought comets were "power rays" of super- natural beings.


They thought a comet contained fire because they are so bright in the sky.


Some people in ancient times thought that a comet was a curse. To save himself from "the curse of the comet," Emperor Nero of Rome had all possible successors to his throne executed.


In 1910, people panicked when a comet passed through Earth's path around the Sun.


In Chicago, people sealed their windows to protect themselves from a comet that they believed had a poisonous tail. Others committed suicide. Special "comet protecting umbrellas", gas masks, and "anti-comet pills" were sold.


Not everyone saw a comet as bad luck. Some thought a comet brought good luck.


They also believed that a comet carried angels through the heavens.



Amazing Space: Online Explorations (NASA) 
"Comets Facts, Myths and Legends" Amazing Space, 2011,