Grammatical gender and noun classes
Does a noun belong to a group that changes other words?
Meaning
Some languages put nouns into groups that make other words take matching forms. These groups may reflect people, animals or shapes, but a noun's group does not always follow its meaning. Some languages have several groups, while others have none or use different pronouns for male and female people without grouping ordinary nouns. Agreement is the matching of forms; Grammatical gender and noun classes is the grouping that can make that matching necessary.
How to spot it
Compare nouns used with the same article, adjective or pronoun, and check whether those words change because the nouns belong to different groups.
In your native language
English nouns do not belong to masculine, feminine or neuter groups that make articles or adjectives change form. English distinguishes gender mainly in pronouns: he and she usually refer to people, while it usually refers to things and often to animals. They can also refer to one person whose gender is unknown or not relevant.
My aunt says she is ready.
She refers to the aunt; the adjective ready has no feminine form.
The door is open. Please close it.
It refers to the door, regardless of whether the word for door has gender in another language.
A customer called, but they didn't leave a name.
They refers to one customer without specifying gender.
In your learning language
Spanish nouns are grammatically masculine (masculino) or feminine (femenino), a grouping that affects the forms of articles, adjectives, and some pronouns. Endings such as -o and -a often help, but exceptions such as la mano and el problema must be learned with their article. This grouping also applies to objects, so it does not simply indicate whether someone is male or female.
El problema parece sencillo.
The problem seems simple.
Problema is masculine despite its -a ending, so it takes el and sencillo.
La mano de Elena está fría.
Elena's hand is cold.
Mano is feminine despite its -o ending, so it takes la and fría.
Compré unas sillas nuevas para la cocina.
I bought some new chairs for the kitchen.
Unas and nuevas both match the feminine plural noun sillas.
Learners whose language has no grammatical gender may leave adjectives unchanged or choose articles without checking the noun. Learners whose language reliably predicts gender from endings may wrongly treat every noun ending in -a as feminine and every noun ending in -o as masculine.