Q: My ESL students are plaguing me for a hard-and-fast rule about using definite or indefinite articles with generalizations. For example, “A computer is a necessary part of modern life” or “The computer is a necessary part of modern life.” Their first language is Russian, which has no articles.
A: This sounds like a simple question but it’s actually quite a tall order. Much about the use of articles in English is idiomatic and defies hard-and-fast rules. (Articles are like prepositions in this sense.) But I’ll give it a try.
Very broadly, “a” (or “an”) is an indefinite article. It’s general. “A boy” means some boy or other, no boy in particular.
“The” is a definite article. It’s specific. “The boy” means a particular boy, or one already referred to.
This is why a first reference to a noun often uses “a” while the second reference to the same noun uses “the,” as in this example: “A boy stood in the doorway. The boy [meaning the one just mentioned] slowly walked over to us.”
But there’s another dimension to “the.” We often use “the” when we use a singular noun in a generic way to refer to all members of a class.
So “the boy” can be used generically to mean something like “all boys.” For example, “As a child psychologist, Dr. Brown has devoted his career to the study of the boy.”
Here it might be easier to switch to animals!
We can correctly say either “A goat is a four-footed animal” or “The goat is a four-footed animal.” But the tendency is to use “the” when referring to a typical example of its class.
And this tendency is stronger the more specific we are about it: “The goat is remarkably nimble and sure-footed.” We don’t mean a particular goat; we mean all goats.
In fact, sometimes you can mentally insert the word “typical” to illustrate this use of “the,” as in “The [typical] goat is remarkably nimble and sure-footed.”
Thus a sentence like “The goat is amazing” is likely to be interpreted not as referring to a particular goat but to the typical one.
It would not be incorrect to say “The goat is amazing” in reference to a particular goat. But a person would be more likely to say “That goat (his goat, this goat, etc.) is amazing.”
You could also use “book” as an example: “A book was on the table. The book [meaning the one just mentioned] lay open.”
When using “book” to represent a class, you could correctly say either “A book is a valuable tool” or “The book is a valuable tool.”
But the more we use the noun as representative of a class, and the more specific we are about it, the more we need “the”: “The book was man’s greatest invention.”
Your computer example is harder to explain. Either of these is grammatically correct and sounds fine to me: “A computer is a necessary part of modern life” or “The computer is a necessary part of modern life.”
But there’s a nuance of difference. “A computer” implies some computer or other, not any one in particular. So an individual is more likely to say (of himself), “A computer is a necessary part of modern life.” In other words, the speaker requires “a computer,” meaning some computer or other.
On the other hand, “the computer” in a sentence like this implies a much broader statement whose subject is a stand-in for computers as a class: “The computer is a necessary part of modern life.”
And the more specific we are about it, the more appropriate “the” seems: “The computer has simplified our lives in many ways and complicated them in others.” Here you don’t mean some laptop or PC or whatever. You use “the computer” to mean “all computers.”
So, using “X” to represent our noun, you could tell your students to use “a” to refer to some X or other, not any X in particular. Use “the” to designate a particular X, or, more abstractly, a generic X that represents all X’s.
I wrote a blog entry last year about other idiomatic uses of “the.” And I wrote one a couple of months later that touches on the different handling of articles in British and American English.
I hope you (and the students) find this helpful.