When do you use que versus quien in Spanish?

que is the default for both people and things, as subject or object, in a defining clause with no preposition: el hombre que vino (the man who came), la casa que compre (the house I bought). quien is only ever for people, and it earns its place in two situations. After a preposition referring to a person: la mujer con quien hablo (the woman I speak with), el amigo a quien escribi (the friend I wrote to). And in a non-defining clause - the kind set off by commas - about a person: mi hermano, quien vive en Madrid, es medico (my brother, who lives in Madrid, is a doctor). In everyday defining clauses with no preposition, use que even for people: el chico que conoci, not el chico quien conoci.

What is the difference between el que and el cual?

Both are article-plus-relative sets that agree in gender and number - el que, la que, los que, las que and el cual, la cual, los cuales, las cuales - and both are used after prepositions to point clearly back at a noun. The difference is register. el que is the everyday choice and also means the one that or the one who: la razon por la que vine (the reason I came), los que llegaron tarde (the ones who arrived late). el cual is the more formal, literary variant, and it comes into its own after longer or heavier prepositions and prepositional phrases: una ley segun la cual todos pagan (a law according to which everyone pays), el puente debajo del cual dormimos (the bridge under which we slept). In speech you will hear el que far more; el cual belongs to careful writing.

How does cuyo work, and what does it agree with?

cuyo is the relative possessive, meaning whose, and it sits directly in front of the thing possessed. The catch that trips everyone up is agreement: cuyo agrees in gender and number with the thing owned, not with the owner. So el autor cuyas novelas leo (the author whose novels I read) - cuyas is feminine plural because novelas is feminine plural, even though the author might be a man. Likewise la mujer cuyo coche vimos (the woman whose car we saw) - cuyo is masculine singular to match coche, not the woman. It has four forms, cuyo, cuya, cuyos, cuyas, and it is a written and formal word; in casual speech people often rephrase with que and a possessive instead.

Spanish Relative Pronouns

A relative pronoun is the hinge that turns two sentences into one. Take Conozco a un hombre and El hombre vino ayer, and the relative pronoun lets you fold them together: Conozco al hombre que vino ayer (I know the man who came yesterday). The que points back at el hombre and saves you repeating it. Every relative pronoun does this same job - it stands in for a noun already named and links the clause that describes it.

Spanish gives you a handful of these words, and the entire skill is picking the right one. Most of the time the answer is que, the workhorse that covers people and things without fuss. The other forms exist for the situations where que alone is not enough: a preposition in front of the gap, a comma setting the clause apart, a whole idea rather than a single noun, or the meaning whose. We will take them one at a time, then boil the choice down to two questions.

que: the workhorse

Que is the default relative pronoun, and it is astonishingly broad. It works for people and things, and it works whether the noun is the subject or the object of its clause. It never changes form.

El hombre que vino es mi tío. (The man who came is my uncle.) - person, subject.
La casa que compré es antigua. (The house I bought is old.) - thing, object.
Los libros que leo son de la biblioteca. (The books I read are from the library.) - thing, object.
La mujer que trabaja aquí habla cinco idiomas. (The woman who works here speaks five languages.) - person, subject.

Notice that English often lets you drop the relative - "the house I bought", not "the house that I bought" - but Spanish never drops que. You must say la casa que compré; la casa compré is not a sentence. If there is a defining relative clause and no preposition in play, que is almost always your answer, and reaching for anything fancier is usually a mistake.

Que also does light preposition work with things, but then it wants an article in front: el libro del que te hablé (the book I told you about), la idea con la que estoy de acuerdo (the idea I agree with). That article set is exactly the el que family below, so it is worth meeting properly.

quien / quienes: people only

Quien (and its plural quienes) refers only to people, never to things. It agrees in number - one person quien, several people quienes - but not in gender. It has two proper homes, and outside them que is preferred.

The first home is after a preposition, pointing at a person:

La mujer con quien hablo es mi jefa. (The woman I am speaking with is my boss.)
El amigo a quien escribí no ha respondido. (The friend I wrote to has not replied.)
Las personas para quienes trabajo son exigentes. (The people I work for are demanding.)

The second home is the non-defining clause - the kind fenced off by commas, adding a detail rather than identifying:

Mi hermano, quien vive en Madrid, es médico. (My brother, who lives in Madrid, is a doctor.)
El director, quien acaba de llegar, quiere hablar contigo. (The director, who has just arrived, wants to speak with you.)

What quien should not do is stand in an ordinary defining clause with no preposition. English "the boy who I met" tempts you toward el chico quien conocí, but Spanish wants el chico que conocí. Keep quien for prepositions and commas.

el que / la que / los que / las que: the article set

This is que with a definite article bolted on the front, and the article makes it agree in gender and number with the noun it stands for: el que, la que, los que, las que. It does two jobs.

First, it gives you a clear, weighty relative after a preposition, especially where you want to pin down exactly which noun is meant:

La razón por la que vine es simple. (The reason I came is simple.)
El motivo por el que lo hice no importa. (The reason I did it does not matter.)
La ventana desde la que miraba estaba rota. (The window I was looking from was broken.)

Second, on its own it means the one that or the one who, packaging an article and a relative into one phrase:

Los que llegaron tarde no entraron. (The ones who arrived late did not get in.)
La que está en la esquina es mi casa. (The one on the corner is my house.)
Este no me gusta; prefiero el que vimos antes. (I do not like this one; I prefer the one we saw before.)

The agreement is the thing to watch: it tracks the noun it replaces, so la razón takes la que, el motivo takes el que, and a plural antecedent takes los que or las que.

el cual / la cual / los cuales / las cuales: the formal variant

El cual and its family are the more formal, written cousins of el que. They agree the same way - el cual, la cual, los cuales, las cuales - and they mean the same thing, but they belong to careful prose and lean speech rarely reaches for them. Where they genuinely earn their keep is after longer prepositions and prepositional phrases, where they read more smoothly than el que:

Una ley según la cual todos deben pagar impuestos. (A law according to which everyone must pay taxes.)
El puente debajo del cual dormimos era antiguo. (The bridge under which we slept was old.)
Las condiciones bajo las cuales firmamos han cambiado. (The conditions under which we signed have changed.)

You will also meet el cual in non-defining clauses in formal writing, where it adds weight and clarity: El informe, el cual fue publicado ayer, es alarmante (The report, which was published yesterday, is alarming). In everyday Spanish you would more likely say que there. Treat el cual as the register dial turned up: correct, precise, and a touch literary.

lo que / lo cual: the neuter relative

The forms above all replace a named noun with a gender. But sometimes what you are pointing at has no gender because it is not a single noun at all - it is a whole idea, a situation, or an unnamed thing. For that Spanish uses the neuter article lo: lo que and lo cual.

Lo que means what in the sense of the thing that, referring forward or back to something unspecified:

No entiendo lo que dijiste. (I do not understand what you said.)
Lo que necesito es un descanso. (What I need is a rest.)
Haz lo que quieras. (Do what you want.)

Lo cual does the same neuter job but refers back to a whole preceding clause - an entire idea just stated - and only appears in non-defining position, after a comma:

Llegó tarde, lo cual me molestó. (He arrived late, which annoyed me.)
No dijo nada, lo cual era extraño. (He said nothing, which was strange.)
Aprobó el examen, lo que alegró a sus padres. (She passed the exam, which delighted her parents.)

The rule of thumb: use lo que when there is no specific noun to point at, and lo que or lo cual interchangeably when you are commenting on the whole idea in the clause before. What you must not do is use que or el que for a genderless idea; llegó tarde, que me molestó is wrong, and it wants lo cual or lo que.

cuyo / cuya / cuyos / cuyas: the possessive whose

Cuyo is the relative that means whose. It sits directly in front of the thing possessed, and here is the trap that catches everyone: cuyo agrees with the thing owned, not with the owner. It has four forms to match the possessed noun in gender and number.

El autor cuyas novelas leo es español. (The author whose novels I read is Spanish.) - cuyas is feminine plural because novelas is, even though the author is a man.
La mujer cuyo coche vimos es famosa. (The woman whose car we saw is famous.) - cuyo is masculine singular to match coche, not the woman.
El país cuyas fronteras cerraron es vecino nuestro. (The country whose borders they closed is our neighbour.)
Un escritor cuyos libros admiro. (A writer whose books I admire.)

Say it out loud and the logic clears up: cuyo behaves like a possessive adjective, so it matches the noun it precedes exactly as mi, tu, su would. The owner's own gender is irrelevant. Cuyo is a formal, written word; in casual speech people often dodge it by rephrasing with que and a possessive. In writing, cuyo is the clean, correct choice, and getting its agreement right marks you out.

The two decisions that drive the choice

Step back from the six forms and the whole system runs on two questions.

First: is there a preposition in front of the gap? If not, and the clause is defining, use plain que - for people and things alike. If there is a preposition, bare que usually will not do: reach for quien/quienes for a person, or el que / el cual (agreeing with the noun) for a thing or for extra clarity. La mujer con quien hablo, la razón por la que vine, la ley según la cual pagamos.

Second: is the clause defining or non-defining? A defining clause identifies which one you mean and takes no commas: el hombre que vino picks out a specific man. A non-defining clause adds a detail you could drop, and it is fenced off by commas: mi hermano, quien vive en Madrid, es médico. Defining clauses lean on que; non-defining clauses about people open the door to quien, and non-defining comments on a whole idea call for lo cual.

Run every relative through those two questions - preposition or not, comma or not - and the correct form is almost always forced.

Worked examples

El profesor que nos enseña es muy paciente. (The teacher who teaches us is very patient.) - defining, no preposition, so que.
La chica a quien di el regalo sonrió. (The girl I gave the gift to smiled.) - preposition plus person, so a quien.
La empresa para la que trabajo está en Madrid. (The company I work for is in Madrid.) - preposition plus thing, so la que agreeing with empresa.
El acuerdo según el cual actuamos ya no existe. (The agreement under which we acted no longer exists.) - formal, heavier preposition, so el cual.
No sé lo que quieres. (I do not know what you want.) - no named noun, so lo que.
Perdió el tren, lo cual arruinó el día. (He missed the train, which ruined the day.) - comment on the whole idea, so lo cual.
La artista cuyos cuadros compramos vive aquí. (The artist whose paintings we bought lives here.) - possessive, agreeing with cuadros, so cuyos.

Common mistakes English speakers make

Dropping que. English happily says "the house I bought", but Spanish never omits the relative. It is la casa que compré, always, with the que in place. If your clause has a subject and verb describing a noun, it needs a relative word.

Using quien in a plain defining clause. "The man who came" tempts you toward el hombre quien vino, but with no preposition and no comma the answer is el hombre que vino. Keep quien for after prepositions and for non-defining, comma-fenced clauses.

Making cuyo agree with the owner. The single biggest cuyo error. El autor cuyo novelas is wrong because novelas is feminine plural - it must be cuyas. Cuyo matches the thing possessed, never the person who owns it.

Using que for a whole idea. When you are commenting on an entire situation rather than a named noun, que and el que will not carry it. Llegó tarde, que me molestó should be llegó tarde, lo cual me molestó. The genderless idea needs the neuter lo que or lo cual.

Forcing el cual into casual speech. El cual is correct but formal. In everyday conversation el que or plain que sounds far more natural: say la razón por la que vine, not la razón por la cual vine, unless you are writing something deliberately formal.

Sort the two questions first - preposition or not, comma or not - and the rest is matching. Que for the ordinary case, quien for people after a preposition or a comma, el que and el cual when a preposition needs an article, lo que and lo cual for a whole idea, and cuyo for whose, agreeing with the thing owned. That is the entire system.