Breakdown of El acertijo es muy difícil de resolver.
ser
to be
muy
very
difícil
difficult
de
linking word before an infinitive (after 'to have just')
Questions & Answers about El acertijo es muy difícil de resolver.
Why do we need the preposition 'de' between 'difícil' and 'resolver'?
In Spanish, when an adjective describes a noun and is followed by an infinitive that acts upon that noun, you must use the preposition de. You cannot link the adjective and the infinitive directly like you do in English with 'to'. So, 'difficult to solve' becomes difícil de resolver.
The lesson calls this a 'passive-like' structure. What does that mean in the context of this sentence?
Look at the relationship between el acertijo (the riddle) and resolver (to solve). The riddle isn't doing the solving; someone else has to solve it. The sentence has a passive meaning ('The riddle is difficult to be solved'), but Spanish uses the active infinitive resolver preceded by de to express this.
Why do we use es (from ser) instead of está (from estar) here? Isn't the difficulty gone once it is solved?
Even though the riddle might eventually be solved, being difficult is considered an inherent, defining characteristic of the puzzle's design, not a temporary physical state or a condition that changes back and forth. Therefore, you use ser.
Would the structure change if we made the sentence plural, like 'The riddles are very difficult to solve'?