The Spanish language has nouns that express concrete objects, groups and classes of objects, qualities, feelings and other abstractions. All nouns have a conventional grammatical gender. Countable nouns inflect for number (singular and plural). However, the division between uncountable and countable nouns is more ambiguous than in English.

Gender

Spanish nouns belong to either the masculine or the feminine grammatical gender.Butt, John, et al. A New Reference Grammar of Modern Spanish. 6th ed., Routledge, 2019. Section 1.1.Kattán-Ibarra, Juan, and Christopher J. Pountain. Modern Spanish Grammar. 2nd ed., Routledge, 2003. Section 2.1.Stein, Gail. Webster’s New World Spanish Grammar Handbook. Wiley, 2015. P. 30. Gender, in this case, refers to a grammatical system and is not necessarily connected with biological sex or gender. For example, la mesa 'table' is feminine despite there being nothing inherently feminine about tables. Adjectives and determiners agree in gender with their associated nouns. In a clause like las mesas grandes son más bonitas 'large tables are nicer', for instance, all adjectives and determiners associated with the head noun (mesas) must agree with it in gender. Mesas is feminine, so the article must be feminine too; thus, las is used instead of los. The two adjectives, whether next to the noun or after the verb, have to agree with the noun as well. Grande 'large' is invariable for gender, so it just takes a plural marker (grandes). Bonito 'nice' can be marked for both gender and number, so bonitas is used with mesas.

The question of whether -o, -a, and similar morphemes are inflectional gender morphemes is a matter of disagreement in grammars of Spanish. For terms like el hijo 'son' and la hija 'daughter', the terms seem to consist of a root like hij- and a suffix -o or-a that determines the noun's gender. But for terms like el escritor 'the (male) writer' and la escritora 'the (female) writer', only the feminine form seems to have an inflectional gender morpheme. Some grammars assume a null gender morpheme for the masculine forms of such terms (e.g., escritor-Ø/escritora) while others argue that such assumptions rely only on theoretical arguments and lack empirical grounds.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.3b.

The masculine gender is inclusive and is used for plural forms of groups of both genders. For example, los niños, grammatically masculine, may mean 'the children' or 'the boys'. The feminine gender is exclusive in the plural: las niñas 'the girls' refers only to girls, not children of both biological sexes or genders. However, some proponents of nonsexist language reform promote alternative forms with desdoblamiento, such as los niños y las niñas or las niñas y los niños.

The manner in which gender is assigned to nouns in Spanish works differently depending on which of two classes the noun belongs to. One class includes certain nouns referring to humans and animals, and the other class consists of nouns not in the first class.

Gender of certain nouns referring to humans and animals Though the gender of most Spanish nouns is assigned arbitrarily, the gender of certain nouns referring to humans and animals are determined by biological sex and gender.Butt, John, et al. A New Reference Grammar of Modern Spanish. 6th ed., Routledge, 2019. Section 1.2.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.1b. For this class of nouns, the masculine and feminine often take different forms. By convention, the masculine form is treated as the lemma (that is, the form listed in dictionaries) and the feminine form as the marked form.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.2a. For nouns of this class with the masculine form ending in -o, the feminine form typically replaces the -o with -a. For example, el abuelo 'grandfather' becomes la abuela 'grandmother'. Exceptionally, some nouns of this class with the masculine form ending in -o lack a distinct feminine form. In these cases, the gender of the noun is marked only by the determiners or adjectives that agree with it. For instance, the feminine form of el soldado 'the (male) soldier' is la soldado 'the (female) soldier', with only the gender of the article (el/la) distinguishing them in this case. For nouns of this class with the masculine form ending in -or, -ón, -ín, -és, and -án, the feminine form adds an -a. For example, el doctor 'the (male) doctor' becomes la doctora 'the (female) doctor'. A few nouns ending in -e also take -a in the feminine such as el jefe and la jefa 'boss' and el presidente and la presidenta 'president'.

The remaining nouns in this class do not typically have distinct feminine forms, but the gender of the determiners or adjectives that agree with them still correspond to biological sex or gender. For instance, el artista refers to an artist who is male while la artista refers to an artist who is female. These nouns are called common gender nouns.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.4a. Other examples include el/la periodista 'journalist', el/la testigo 'witness', and el/la estudiante 'student'.

For some nouns in this class called heteronyms (heterónimos), the masculine and feminine forms are distinct lemmas. Much as English has the distinct lemmas bull and cow, for example, Spanish has the distinct forms el toro 'bull' and la vaca 'cow'. For these nouns, the masculine plural form is typically used for groups containing both male and female members. A group containing both actors (los actores) and actresses (las actrices), for instance, is referred to as los actores 'actors'.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.1g. Exceptionally, an animal species may be represented by the feminine lemma rather than the masculine (much as the English goose can refer either to the species as a whole or specifically females of the species when contrasted with gander). For example, la vaca can refer to the species 'cattle' or the female of the species 'cow', but el toro refers only to the male of the species 'bull'.

Notably, not all nouns that refer to humans and animals belong to this class of noun; thus, not all nouns that refer to humans and animals take different forms for the masculine and feminine. For example, la persona 'person' does not belong to this class and is always feminine, regardless of the sex or gender of the person. Similarly, la araña 'spider' does not belong to this class and is always feminine, regardless of the sex of the spider.Butt, John, et al. A New Reference Grammar of Modern Spanish. 6th ed., Routledge, 2019. Section 1.3.

Gender of other nouns In Spanish, nouns not belonging to the class described above form another class of noun. The gender of nouns in this other class are arbitrarily assigned. However, some general patterns help to predict the gender of nouns.Kattán-Ibarra, Juan, and Christopher J. Pountain. Modern Spanish Grammar. 2nd ed., Routledge, 2003. Section 2.3. Notably, the endings of nouns give clues to their genders. For instance, nouns ending in -o are usually masculine.Batchelor, R. E., and Miguel Ángel San José. A Reference Grammar of Spanish. Cambridge UP, 2012, https://doi.org/10.1017/CBO9780511845604. Section 9.2.2. The exceptions are la dínamo 'dynamo' (also el dínamo in Latin America), la disco 'disco', la foto 'photo', la líbido 'libido', la magneto 'magneto' (also el magneto), la mano 'hand', la moto 'motorcycle', and la radio 'radio' (also el radio in Latin America). Words ending in -aje, -or, -án, -ambre or a stressed vowel are also typically masculine. The exceptions are la flor 'flower', el hambre 'hunger', la labor 'labor', and la pelambre 'patch of hair' (also el pelambre). Nouns ending in -men or -gen are also often masculine, but there are exceptions, such as la imagen 'image'.Batchelor, R. E., and Miguel Ángel San José. A Reference Grammar of Spanish. Cambridge UP, 2012, . Sections 9.2.6–9.2.7. Finally, nouns that both end in -ma or -eta and are derived from Greek are typically masculine.

Many grammars of Spanish suggest that nouns ending in -a are feminine,Batchelor, R. E., and Miguel Ángel San José. A Reference Grammar of Spanish. Cambridge UP, 2012, . Section 9.3.2.Stein, Gail. Webster’s New World Spanish Grammar Handbook. Wiley, 2015. P. 32. but there is no requirement that Spanish nouns ending in -a be feminine. Thus, grammars that pose such a requirement also typically include a long list of exceptions, such as el alerta 'alert', el bocata 'sandwich', el caza 'fighter plane', and many others. More reliable markers of feminine nouns are -ez, -eza, -ción, -ía, -sión, -dad, -tad, -tud, -umbre, -ie, -nza, -cia, -sis, and -itis. The exceptions for -ez are el ajedrez 'chess' and el pez 'fish', and the exceptions for -sis are el análisis 'analysis', el éxtasis 'ecstasy', el apocalipsis 'apocalypse', el paréntesis 'parenthesis', and el énfasis 'emphasis'.

Though the gender of nouns in this class does not correspond to biological sex, it can mark other kinds of differences. For example, gender marks the difference between a tree (typically masculine) and its fruit (typically feminine). Thus, el almendro and el cerezo refer to 'almond tree' and 'cherry tree', respectively, while la almendra and la cereza refer to 'almond' and 'cherry', respectively.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.3g. In many cases, these patterns with specific nouns can be traced to a common hypernym.Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.10a. For example, el almendro and el cerezo are masculine because the hypernym el árbol 'tree' is masculine. The following table lists some of these patterns.

{| class="wikitable sortable" !Class !Gender !Example !Hyponym !Reference |- |automobiles |masculine |un Mercedes |el automóvil |Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.1c. |- |cardinal directions |masculine |el Sur |el punto cardinal |Stein, Gail. Webster’s New World Spanish Grammar Handbook. Wiley, 2015. P. 31. |- |centuries |masculine |el XV |el siglo

|colors |masculine |el azul |el color

|companies |feminine |la Mercedes |la empresa

|days |masculine |el lunes |el día

|fruits |feminine |la cereza |la fruta

|highways |feminine |la Nacional IV |la carretera |Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.1e. |- |hours |feminine |las cuatro |las horas

|islands |feminine |las Canarias |la isla |Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.1d. |- |lakes |masculine |el Titicaca |el lago

|languages |masculine |el ruso |el idioma

|letters |feminine |la eme |la letra

|months |masculine |el agosto |el mes

|motorcycles |feminine |una Vespa |la motocicleta

|mountains |masculine |los Alpes |el monte

|numbers |masculine |el cuatro |el número

|oceans |masculine |el Pacífico |el océano

|rivers |masculine |el Amazonas |el río

|seas |masculine |el Cantábrico |el mar/la mar

|sports teams |masculine |el Peñarol |el equipo |Nueva gramática de la lengua española. Real Academia Española, 2009. Section 2.10i. |- |trees |masculine |el cerezo |el árbol

|years |masculine |el 1999 |el año

The gender of nouns in this class may also mark distinctions related to size and shape, such as the distinction between el cántaro 'pitcher' and la cántara 'large pitcher'. Further, some polysemic nouns can be distinguished by their gender. For example, el margen (masculine) means 'margin' while la margen means 'river bank'.Kattán-Ibarra, Juan, and Christopher J. Pountain. Modern Spanish Grammar. 2nd ed., Routledge, 2003. Section 2.4. Similarly, el cura (masculine) means 'priest' while la cura means 'cure'.Stein, Gail. Webster’s New World Spanish Grammar Handbook. Wiley, 2015. P. 34.