What does "que" and "cual" mean without an accent mark? How do they compare when to each other? How do they compare to their accent-marked form?
Qué and cuál are interrogatory pronouns, and are thus used when asking questions (see relevant question):
¿Qué ha ocurrido? → What has happened?
¿Cuál es tu número de teléfono? → What is your phone number?
Qué can also be an exclamative adjective (if it is used before a noun):
¿Qué hora es? → What time is it?
Qué can also be an exclamative adverb (if it is used before an adjective):
¡Qué guapa es! → How pretty she is!
Qué can also be used in exclamations (not only in questions). So qué (with accent mark) can be used in direct or indirect questions and exclamations:
¿Qué has hecho? → What have you done?(direct question)
No sé qué hacer. → I don't know what to do. (indirect question)
¡Qué guapa es! → How pretty she is! (direct exclamation)
Ya sabe qué dura es la vida. → He already knows how hard life is. (indirect exclamation)
Without accents, they are relative pronouns:
Rebeca es la mujer con la que vas a viajar. → Rebeca is the woman with whom you are going to travel.
Rebeca es la mujer con la cual vas a viajar → Rebeca is the woman with whom you are going to travel.
Que (without the accent) can also be a conjunction:
Quiero que vengas. → I want that you go. / I want you to go.
Llámame antes de que llegues. → Call me before you arrive.
(1) "Que" (without accent) is equivalent to "that". For example:
I guess that you are Anne.
Supongo que eres Anne.
(2) "Cual" (without accent) is quite equivalent to "whom". For example:
Anne is the woman whom Jhon got married.
Anne es la mujer con la cual Jhon se casó.
(3) Their accent marked form is used when asking. All interrogatory pronouns in spanish have accent (e.g. qué, cuál, cómo, dónde). For example:
¿Cuál es tuyo?
Which is yours?
¿Qué es eso?
What is that?
This also applies to the defining or non-defining relative clauses.
We use que for the relative pronouns who & which:
- This is the nurse who helped me = Esta es la enfermera que me ayudó.
- This is the farm which was built in 1978 = Esta es la granja que se construyó en 1978.
However, this can be even more complicated because we introduce que in clauses where English sentences don't have them:
- I think I'll go = Creo que iré.
Considering that que often triggers the subjunctive in present or past depending of the context:
- I asked you to bring it = Te pedí que lo traigas/trajeras.
In this case, verb + object + infinitive often triggers a que in a Spanish sentence. We could also have te pedí traerlo, invoking the infinitive and no que is shown.