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Hi there,
I thought that ordinal numbers can have only a definite article. Then I read one post yesterday from a native speaker where he used indefinite article...
"A second text file was used to pry it open"
Why he used indefinite article?
I've also found out that ordinal numbers don't need to have an article at all.
When is then used definite, when indefinite and when zero article with oridnal numbers?
Comments  
In most cases the definite article is used because the number makes the object in question specific

However, sometimes you'll find "a second", "a third" e.t.c. They all mean another (an+other).

As to zero article, I do not know. You mean numerals or numbers?
DamirI thought that ordinal numbers can have only a definite article.
There is no such rule.
You are learning English as *a* second language, aren't you?
A second look. A second opinion. A second chance.
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She started learning English as a second language when she was eight. English is her second language. English is the second most popular first language on the planet. Speaking English is now like second nature to her.
To determine if you need an article and what article to use, take away the ordinal numbers and see what or if articles are required. Of course, by taking away the ordinal numbers, you change the meaning of the sentence, but this is an easy way to check if your sentence is grammatical.
So the way to determine an article is to remove a number and see which one fits. Thanks Pter[Y]