Which article should be used in this example?
closed as off-topic by Dan Bron, Edwin Ashworth, Hellion, Robusto, ScotM Mar 11 '15 at 2:41
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Both are grammatically correct. Your choice rests upon the context in which you are using the clause.
the prime indicator of success
This implies that there is only one prime indicator of success.
a prime indicator of success
This implies that there could be more than one indicator of success that could be considered prime.
The prime indicator of success = this/that prime indicator of success.
A prime indicator of success = some/any prime indicator of success.
I'd argue that there is only one prime indicator, and I would therefore use the definite article. This is not borne out by common usage, however. You just need to decide if "prime indicator" is unique or if it can be plural. If plural, the indefinite "a" is grammatically correct.
Either is acceptable given your usage.
Consider the text used to define these words:
the (article). A definite grammatical article.
a (article). The indefinite grammatical article.
When you say "a specific blah" or "a prime blah," you are using the article in a definite manner, thus
a prime are synonymous.