For the language student, to learn Spanish is also to be aware (and stay clear) of the common grammatical mistakes most beginners commit. This is not to say never to commit mistakes but knowing them lessens the chances of making errors.
Prepositions
Prepositions in English and Spanish do not usually have a one-on-one agreement. A simple English preposition such as IN might be translated not only as EN but also as DE (as in DE LA MAANA for in the morning).
DE is typically translated as OF or FROM.
Adjectives
In English, possessive adjectives are used to refer to body parts or articles of clothing. In Spanish, the definite articles EL or LA is used when the person or the owner of the body part or the item is obvious.
The correct Spanish for Open your eyes! is ABRE LOS OJOS! (The literal back translation would come out as Open THE eyes!)
Gender
One very common mistake in a Spanish lesson is forgetting the gender. An example is forgetting the feminine counterpart in numbers when it is needed. For a masculine noun, we say CUATRO CIENTOS TREINTA Y DOS for 432, but it is CUATRO CIENTAS Y DOS when referring to a feminine noun.
It is easy to forget because the number is a long way off from the noun. Here is a correct example: TENGO QUINIENTAS DIECISEIS GALLINAS. (I have 516 hens.)
Articles
Normally, UN OTRO or UNA OTRA mean another. However, this indefinite article is not needed in Spanish. Neither one is needed before CIERTO, which means a certain. Correct are QUIERO OTRO LIBRO (I want another book.) and QUIERO CIERTO LIBRO. (I want a certain book.)
Be careful in using UN or UNA when referring to occupation. The articles A or AN are required in English but are not used in Spanish. You say, NO SOY MARINERO, SOY CAPITN. (I am not a mariner, I am a captain.)
A definite article is usually used for days of the week (singular EL and plural LOS). The correct way of saying I work on Mondays is TRABAHO LOS LUNES.
Ending in prepositions
In English, it is common to end sentences in prepositions, although grammarians frown on this.
In Spanish, it is completely forbidden. The correct way of saying Whom can I eat with? is CON QUIEN PUEDO COMER?
Quien and que
Sometimes, QUIEN is also used wrongly in relative clauses to mean who. In English, we say The car THAT runs and The boy WHO runs.
In Spanish, QUE is used to mean both THAT and WHO. A correct sample is the following sentence. MI HIJA ES ALUMNA QUE ESTUDIA MUCHO. (My daughter is a student who studies a lot.)
Redundant words
Here is a marked difference between English and Spanish redundancies that are required in Spanish but which would be incorrect in English. The following samples feature a redundant direct object that has double (and triple!) negatives. JUAN LE DA UNA CAMISA A EL. (John is giving a shirt to him.) NO DIJO NADA. (He said nothing.)
To learn Spanish is to deftly avoid these grammatical mistakes, if possible. Sometimes, however, making mistakes is the only way to learn.