The basic rule: The rule that you follow most of the time is roughly the same as the rule in English: If a word ends in a consonant, add <em>-es</em>. If it ends in an unaccented vowel, simply add an <em>-s</em>. In Spanish, <em>y</em> is treated as a consonant for purposes of pluralization.
<ul>Examples: <em>un árbol</em> (one tree), <em>dos árboles</em> (two trees), <em>el actor</em> (the actor), <em>los actores</em> (the actors), <em>el hotel</em> (the hotel), <em>los hoteles</em> (the hotels), <em>un taco</em> (a taco), <em>dos tacos</em> (two tacos), <em>un perro</em> (a dog), <em>tres perros</em> (three dogs), <em>un rey</em> (a king), <em>cuatro reyes</em> (four kings). </ul>
Orthographic changes: Some words follow the general rule in terms of pronunciation, but a change in either a letter or an accent mark is needed. In plurals of words that end in <em>-z</em>, the <em>-z</em> changes to <em>-ces</em> for the plural. And if the addition of <em>-es</em> would change which syllable gets the accent, an accent is either dropped or added.
<ul>Examples: <em>el juez</em> (the judge), <em>los jueces </em>(the judges), <em>una vez</em> (once), <em>dos veces </em>(twice), <em>el inglés</em> (the Englishman), <em>los ingleses</em> (the Englishmen), <em>la canción </em>(the song), <em>las canciones </em>(the songs), <em>el examen</em> (the exam), <em>los exámenes</em>, the exams. </ul> Words ending in stressed vowels: Words that end in a stressed <em>-é</em> form the plural simply by adding <em>-s</em>. Words that end in other stressed vowels have an <em>-es</em> added. There are four common exceptions: <em>el papá</em> (the father), <em>los papás</em> (the fathers), <em>una mamá</em> (a mother), <em>dos mamás</em> (two mothers), <em>el dominó</em> (the domino), <em>los dominós </em>(the dominoes), and <em>un sofá</em> (a sofa), <em>tres sofás</em> (three sofas). <ul>Examples: <em>el rubí</em> (the ruby), <em>los rubíes</em> (the rubies), <em>el hindú</em> (the Hindu), <em>los hindúes</em> (the Hindus), <em>el café</em> (the coffee), <em>los cafés</em> (the coffees). </ul> Finally, the exceptions: The above rules cover probably 99 percent of the nouns you will use. Most of them are words that are identical in the singular and plural — e.g., <em>la crisis</em> (the crisis), <em>las crisis</em> (the crises) — and new words of foreign origin, which often follow the pluralization rules of the originating language — e.g., <em>el applet Java</em> (the Java applet), <em>los applets Java</em> (the Java applets). As a beginner, the main exceptions you need to know are the days of the week, Monday through Friday, which are the same in singular and plural — <em>los lunes</em> (Mondays), <em>los martes</em> (Tuesdays), and so on.