Different occurrences of “que”, “qu'” or “qui” in questions

Question

Qui est-ce ___ parle ?

What should the blank be filled with?

• que

• qu'

• qui

I am really confused about this! Is there an explanation?

Answer 1

Here are example of correct uses of "qui" and "que" :

Qu'est-ce que tu en penses ? (What do you think ?)

Qui est-ce qui parle ? (Who's talking ?)

"Qu' " is the form of "que" used before a vowel, like in "qu'est-ce que ...", or in "qu'est ce qu' il en pense ?"

Sometimes the first pronoun is the same as the second one (assuming "qu' " == "que"), but it's not always the case.

When it is, you can phrase these sentence to use only one pronoun, though it's a little too formal for casual conversation :

Qu'en penses-tu ?

Qui parle ?

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Edit : As Stéphane mentioned, there are other cases, when this doesn't work :

Qu'est-ce qui est rond et rouge ?

This phrasing is typical in riddles for example.

In the last sentence, we're still talking about and object, but there's a difference : "Qu'est-ce" is the subject, to the verb "être" : "Il est rond est rouge".

While in the first sentence, "Qu'est-ce" is the complement, while tu is the subject : "Qu'est-ce que tu en penses ?".

So here is the rule: qui follows the subject of the verb, while que/qu' follows the complement.

My apologies for my hasty and incorrect first answer.

Answer 2

“Qui est-ce ?” when speaking to somebody and indicating someone means you want information on this someone.

“Qui est-ce qui parle ?” is the exact same question except that you indicate this someone by the fact that he is speaking right now.

Answer 3

FR: qu'est-ce qui / qu'est-ce que / qui est-ce qui / qui est-ce que | WordReference Forums

The first que/qui tells you whether the answer to your question will be a person (qui) or an thing (que).
The second que/qui tells you whether the answer to your question will be the subject or the object.

QUI
SUJET: Qui est-ce qui mange? Il mange.
OBJECT: Qui est-ce que vous aimez? J'aime James.

QUE
SUJET: Qu'est-ce qui te fait mal? Mon dos me fait mal.
OBJET: Qu'est-ce que vous voulez? Je veux un chaton.

When you have Qui...qui or Que...que, you can omit the est-ce part:

Qui est-ce qui mange? → Qui mange?
Qu'est-ce que vous voulez? → Que voulez-vous?