Keeping Prepositions Before "que"
In Spanish, many verbs and adjectives are paired with a specific preposition, like de, en, or a. When you connect these expressions to a subordinate clause starting with que (that), you must keep the preposition right in front of que.
While English often drops prepositions here ("I realized that..." instead of "I realized of that..."), dropping them in Spanish is a grammatical error.
Expressions with "de que"
Expressions involving mental states, memories, or emotions often require de—such as darse cuenta de (to realize), acordarse de (to remember), and estar consciente de (to be aware of). When followed by a clause, use de que.
Expressions with "en que"
Verbs expressing persistence, trust, or focus often pair with en—like insistir en (to insist on), confiar en (to trust), and enfocarse en (to focus on). Keep the en exactly where it belongs: right before que.
Expressions with "a que"
The same rule applies to verbs that take the preposition a, such as acostumbrarse a (to get used to). Even if it feels redundant, do not drop the a before a que clause.