Breakdown of Dudo que ellos hayan descifrado el acertijo.
ellos
they
que
that / than
haber
(auxiliary) have
dudar
to doubt
descifrar
to decipher
el acertijo
the riddle
Questions & Answers about Dudo que ellos hayan descifrado el acertijo.
Why do we use hayan descifrado here instead of a simple past tense like descifraron?
The phrase Dudo que (I doubt that) expresses uncertainty, which forces the second part of the sentence into the subjunctive mood. Because the action of deciphering is something they supposedly already did, we use the present perfect subjunctive (hayan plus the past participle) to say that they have deciphered it.
If I changed the sentence to say I am sure that they have deciphered the riddle, would I still use hayan?
No, you would not. Phrases expressing certainty, like Estoy seguro de que (I am sure that) or No dudo que (I do not doubt that), trigger the normal indicative mood. You would instead use the regular present perfect: Estoy seguro de que ellos han descifrado el acertijo.
Is it strictly necessary to include the pronoun ellos in this sentence?
I see that descifrado looks a lot like deciphered. Is it a regular verb?
Yes, descifrar (to decipher or decode) is a regular verb. You form its past participle simply by taking off the -ar ending and adding -ado. Just like in English, it shares a root word related to codes or ciphers, which is cifra in Spanish.
Can I use the word acertijo to talk about putting together a jigsaw puzzle?
No, acertijo specifically refers to a riddle, a brain teaser, or a verbal puzzle. If you want to talk about a physical jigsaw puzzle, you would use the word rompecabezas (which literally translates to head-breaker).
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