Verbs with fixed prepositions: negarse a, contar con, fijarse en...

What these expressions are (and why they matter)

All items in the table are fixed verb + preposition combinations. At B2 level, accuracy here matters because:

• The preposition is not optional.
• Changing it usually makes the sentence sound non-native or incorrect.
• Some of them are pronominal (they require se and it must agree with the subject).

Quick map: which ones take an infinitive vs a noun

The pronominal ones: don’t forget se

Three of these are typically used with se (and it changes with the subject):

• decidirse a (to decide to, after some hesitation)
• negarse a (to refuse to)
• echarse a (to suddenly start doing something)
• darse cuenta de (to realize)
• fijarse en (to notice / pay attention)

Agreement check (match the subject):

Meaning and “when to choose which” (high-yield contrasts)

• Decidirse a = making the choice, often after doubt.
  • Se decidió a hablar por fin. (He finally decided to talk.)
• Negarse a = refusing (active resistance).
  • El testigo se negó a firmar la declaración.
• Echarse a = sudden start (dramatic / immediate).
  • Al oír la sirena, se echó a correr.
• Contar con = rely on / have as support.
  • Para el informe, contamos con el peritaje.
• Darse cuenta de = realize (a mental “click”).
  • Se dio cuenta de que el documento era falso.
• Fijarse en = notice by paying attention (you look carefully).
  • Fíjate en la firma: no coincide.
• Reparar en = notice (more formal; often with no).
  • No reparó en el micrófono oculto.

The fixed preposition: common mistakes to avoid

• Negarse always needs a + infinitive:
  • Se negó colaborar. → Se negó a colaborar.
• Fijarse takes en (not a, not de):
  • Se fijó a la huella. → Se fijó en la huella.
• Darse cuenta takes de:
  • Se dio cuenta en la mentira. → Se dio cuenta de la mentira.
• Contar changes meaning without con:
  • contar con = rely on / have available
  • contar (without con) = to count / to tell (a story)

Mini self-check (before you speak or write)

1. Is this one pronominal? If yes, did I match me/te/se/nos/os/se to the subject?
2. Did I keep the fixed preposition? a / con / de / en
3. What comes next?
   • a → usually an infinitive (negarse a colaborar)
   • con / de / en → usually a noun (con pruebas, de la mentira, en la huella)
4. Do I want “sudden start”? If yes, prefer echarse a (se echó a correr).

Useful ready-to-use chunks (professional, natural)

• Nos negamos a aceptar esa condición.
• Cuento con tu discreción.
• Me di cuenta de que faltaba una página del informe.
• Fíjate en este detalle antes de enviar el correo.
• No reparé en ese dato durante la reunión.