Pitman's Commercial Spanish Grammar (2nd ed.)

The Definite Article is used in Spanish and not in English (besides rules given in Lesson II) --

1. Before the seasons of the year --

 La primavera (spring)       El otoño (autumn)
 El verano (summer)          El invierno (winter)

And the four cardinal points --

 El norte (North)            El este (East)
 El sur (South)              El oeste (West)

2. Before the hour of the day (with the words hora, horas, understood), as --

Es la una: It is one o'clock.
Son las dos y cuarto: It is a quarter past two.
Son las tres y cinco: It is five minutes past three.
Son las cuatro menos diez: It is ten minutes to four.
Las cinco y media: Half-past five.

3. Optionally, before the proper name of a woman used colloquially, as --

La Maria (Mary, our Mary).

4. Optionally, before the days of the week, especially when preceded by "on" in English, as --

Vendré el sábado: I shall come on Saturday.

5. Before the names of the following countries --

El Perú, La India, El Japón.

And some towns to be learnt by practice, as --

La Coruña, El Havre, El Cairo, El Ferrol, etc.

Although found sometimes before the names of countries in general, this example should not be followed.

The Definite Article is used in English and not in Spanish --

1. Before numbers following names of sovereigns, etc., as --

Carlos I (primero), Charles I (the first)
Alfonso XIII (trece), Alphonso XIII (the thirteenth)

2. In titles of books, headings, etc., as -- Historia de la Inquisición (The History of the Inquisition).

3. Before words in apposition, as -- Madrid, capital de España (Madrid, the capital of Spain).

But --

Alfonso el Sabio (Alphonso the Wise)
Juana la Loca (Jane the Mad)
because these are "titles."

The Indefinite Article is used in English and not in Spanish (besides rules in Lesson II) --

1. Before words in apposition, as --

Rubio y Cía., casa importantísima de la Habana: Rubio & Co., a most important firm in Havana.

2. In titles of books, headings, etc., as --

Lista de los géneros pedidos: A list of goods required.

3. In "such a," "so ... a," as --

Tal amigo: Such a friend.
Tan buen amigo: So good a friend, such a good friend.

4. In "a half" (medio), "a quarter" (cuarto), "a third" (tercio), in the case of an integer preceding, as -- Uno y medio (1-1/2) Cinco y tercio (penknife/3) Dos y cuarto (2-1/4)

Occasionally the article is omitted before other fractions.

5. Before otro, as --

Otra quiebra: Another bankruptcy.

Before weights and measures the definite article is used in Spanish instead of the indefinite used in English, as --

Dos chelines la libra: Two shillings a pound.
Cinco pesetas el metro or por metro: 5 pesetas a metre.

The Definite Article is omitted before casa and palacio when they are spoken of as places usually frequented by the person in question --

Iré á casa del ingeniero: I shall go to the engineer's house.
El Rey volvió ayer a palacio: The King returned yesterday to the palace.

The article must not be employed before a noun used after a preposition in an adjectival capacity, as --

Una viga de hierro (not del hierro): An iron beam.

The tendency of the Spanish language is to omit the indefinite article whenever, by such omission the sense is not obscure, as --

Tengo intención de marcharme: I have a mind to go.
Vino con dolor de cabeza: He came with a headache.
Le dió cuenta de lo sucedido: He gave him an account of all that had happened.
Este caballero tiene mucho or grande ingenio: This gentleman has a great talent.

The Neuter article lo cannot precede a noun used as such, but it may (elegantly) precede a noun used adjectively, as --

Todo me gusta en el, lo amigo, lo ciudadano, lo caballero:

I like everything in him: the friend, the citizen, the gentleman.