How do you know when to use definite or indefinite articles?

Question

I know that the definite articles all mean "the," and the indefinite articles mean "a" or "an." Is there a set way to use either the definite or indefinite articles? Or, are the definite and indefinite articles interchangeable like in English?

For example, in English, I can say "a salad" or "the salad."

Can I also interchange the articles in Spanish too, to say: "Una ensalada" or "La ensalada?"

Answer 1

I think it is used in a similar manner in both languages. If there are five salads on a table and I tell you to take a salad, I mean take any one. If I tell you to take the salad then I am indicating a specific salad, probably one we were already discussing.

Isn't that what I said? :) - Benz, JUL 9, 2010

Yes basically, I figured I would elaborate. Also she is new to the forum, the more answers and/or reinforcement the better. - Jsanthara, JUL 10, 2010

Answer 2

"una ensalada" -- any salad , cualquier ensalada

"la ensalada" -- a specif one, una específica