Articles are used before nouns to indicate a subject's number or gender. Sometimes, however, the use of an article before a noun is not required. This happens with both indefinite and definite articles, in Spanish, in English and in many other languages as well. In fact, generally speaking, articles are used the same way in Spanish and English. There are many cases in which the same rules apply for both languages. For example, you don't use definite articles before days of the week or months following the verb ser (to be):
Hoy es viernes. Son las siete de la tarde.
Today is Friday. It's seven in the evening.
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or following the preposition de (from):
Trabajo de lunes a sábado.
I work from Monday to Saturday.
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It's not very common, and even unnecessary, but you could use indefinite articles in both cases. The meaning is slightly different and this happens both in Spanish and English:
Hoy es un miércoles / Hoy es miércoles.
Today is a Wednesday / Today is Wednesday.
Es la misma rutina de un lunes a un viernes / Es la misma rutina de lunes a viernes.
It's the same routine from a Monday to a Friday / It's the same routine from Monday to Friday.
However, there are a few cases in which we wouldn't use "a" or "an" in English, but we would in Spanish and vice versa. For example, in Spanish you can use a definite article before days and say Los lunes no trabajo (I don't work on Mondays) or Estoy esperando desde el lunes (I've been waiting since Monday). These you need to learn, so let's explore some examples.
In Spanish, you can drop indefinite articles when the noun is preceded by words like tal[es] (such), otro/a (other), and qué (what). Compare with the English translation in the following examples:
Qué lástima que no llegaste al partido; estuvo joya.
What a pity that you didn't come to the game; it was awesome.
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...de cierta manera... con ciertos defectos, ¿no?
...in a certain way... with certain defects, right?
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In the previous example English drops the article when using the plural only, while Spanish drops it in both singular and plural. And yet, saying de una cierta manera in Spanish is also correct.
Spanish doesn't use definite articles before numerals that express titles of rulers:
El edificio data del siglo dieciocho,
The building dates from the eighteenth century,
en tiempos de Felipe Quinto.
during the time period of Philip the Fifth.
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In Spanish you usually drop definite and indefinite articles before nouns in apposition (when a noun explains another). But you don't necessary want to do it every single time. For example, in Spanish you can say Ankara, capital de Turquía, es una bella ciudad (Ankara, the capital of Turkey, is a beautiful city.) However, it's still correct to say Ankara, la capital del Turquía, es una bella ciudad. Obviously, in this case you can't use the definite article. You can't say Ankara, una capital de Turquía—that doesn't make sense either in Spanish or English since cities have, by definition, only one capital.
But check out this example: Juanita, una tía de Raquel, vino de visita (Juanita, one of Raquel's aunts, came to visit). Saying Juanita, tía de Raquel, vino de visita (Juanita, Raquel's aunt, came to visit) is also correct. And Juanita, la tía de Raquel, vino de visita is correct too. The translation in English is the same: Juanita, Raquel's aunt, came to visit. The only difference is that the definite article la (the) confers some sense of specificity to the expression. Maybe it means that Juanita is the only aunt Raquel has, or that she is particularly close or somehow special, she is not just any aunt but la tía (the aunt).
In Spanish you usually drop indefinite articles before unmodified nouns when stating nationality, profession, and religious or political affiliation. You can't always do the same in English. For example:
El Señor Chong es mexicano. Es burócrata. Es Secretario de Gobernación. Es católico. Es priísta.
Mr. Chong is Mexican. He is a bureaucrat. He is Secretary of State. He is a Catholic. He's an affiliate of the PRI party.
Here is another example from our catalog:
Y ¿tu marido es agricultor o algo?
And your husband is a farmer or something?
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That doesn't mean that saying mi marido es un agricultor (my husband is a farmer) is wrong. It's just not the way you usually state professions. On the other hand, when the noun is modified (usually by an adjective or a subordinate clause), you have to use an article. For example, you must say: mi marido es el agricultor famoso (my husband is the famous farmer) or mi marido es un agricultor que se preocupa por el medio ambiente (my husband is a farmer who cares about the environment).
What is really incorrect is not using articles before the names of languages. When talking about languages, English usually drops the articles, but Spanish doesn't:
El español es un idioma muy bonito.
Spanish is a very nice language.
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There's an exception. You can drop the article when the language is used directly after a verb as its complement:
Como... como yo hablo árabe.
Since... since I speak Arabic.
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Finally, don't drop the article when telling the time in Spanish. You will always use the feminine definite article la or its plural las, since it refers to la hora (the hour) or las horas (the hours).
Salí a las siete y media... y voy llegando a la una.
I went out at seven thirty... and I'm arriving at one.
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