What is the difference between "al" and "a la"?

Question

Consider the following sentence:

Vamos a entender a la maestra. (We are going to understand the teacher)

I remember seeing in a similar sentence the word al being used instead of a la. So are these two ways of referencing the person interchangeable? Or are there specific contexts in which one must be used over the other?

Answer 1

Vamos a entender a la maestra.

In the case of a la maestra, la is a definite article (femenino singular->feminine singular) that you put before of a noun to indicate this noun is known to the speaker.

Vamos a entender al maestro.

al is the contraction of a el and el is a definite article (masculino singular->masculine singular) that you put before of a noun to indicate this noun is known to the speaker. Unlike in English, where contractions are optional (will not and won't are grammatically interchangeable), the use of the contraction al is obligatory in Spanish (as is the contraction del, which means de el), except when the el is part of a proper noun:

• Vamos a El Salvador. NOT Vamos al Salvador.

Also be sure not to confuse el (it) with él (him/he). a él is never shortened:

• Vamos a verlo a él.

There are five definite articles in Spanish:

• Masculine singular -> el
• Masculine plural -> los
• Feminine singular -> la
• Feminine plural -> las
• Neuter singular -> lo

Note that although in Spanish nouns are either masculine or feminine, it is possible to use the definite article lo to construct a neuter form. For example:

Me gusta lo francés

I like French things

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Feel free to edit if you see any errors in my attempt in English.

Hope this helps.