Using "por si/por si acaso" for "in case" (subordinate conditional clause)

Question 1

Por si and por si acaso

Answer 1

are interchangeable. In Spanish we use “por si” or “por si acaso” to express “in case/just in case [something happens]”.

They introduce a subordinate clause expressing a condition. They can be followed by the subjunctive or the indicative.

With the indicative - more probable

With the subjunctive - less probable

Question 2

I am taking the umbrella in case it rains.

Answer 2

Me voy a llevar el paraguas por si llueve.

Question 3

Here is the money I owe you, in case I forget later.

Answer 3

Toma el dinero que te debo, por si acaso se me olvida después.

Question 4

I explained the lesson again in case they hadn’t understood.

Answer 4

Expliqué de nuevo la lección por si no les había quedado claro.

Question 5

You must not tell Roberto about any of this, in case he asks you.

Answer 5

No debes decirle nada de esto a Roberto, por si acaso te pregunta.

Question 6

I am taking the umbrella in case it rains (less probability)

Answer 6

Me voy a llevar el paraguas por si lloviera.

Question 7

Here is the money I owe you, in case I forget later. (less probability)

Answer 7

Toma el dinero que te debo, por si acaso se me olvidase después.

Question 8

I explained the lesson again in case they hadn’t understood. (less probability)

Answer 8

Expliqué de nuevo la lección por si no les hubiera quedado claro.

Question 9

You must not tell Roberto about any of this, in case he asks you. (less probability)

Answer 9

No debes decirle nada de esto a Roberto, por si acaso te preguntara.

Question 10

If the main clause uses a tense that implies a future action, for example El Imperativo or El Futuro Simple,

Answer 10

then the por si/por si acaso clause uses El Presente (probable) or El Imperfecto Subjuntivo (less probable)

Question 11

I will give him the money I owe him, in case I forget later.

Answer 11

Le daré el dinero que le debo, por si acaso se me olvida después.

Question 12

Put the wellies on in case it rains.

Answer 12

Poneos las botas de agua por si lloviera.

Question 13

If the main clause uses a tense that implies a past action, for example El Pretérito Indefinido or El Pretérito Pluscuamperfecto,

Answer 13

then the por si/por si acaso clause uses a past tense.

Question 14

I gave him the money I owed him just in case I forgot later.

Answer 14

Le di el dinero que le debía por si acaso se me olvidaba después.

Question 15

We put our wellies [US: rain boots] on in case the path was very muddy.

Answer 15

Nos pusimos las botas de agua por si el camino estaba muy enfangado.

Question 16

She had left his dinner in the oven just in case he had not eaten anything during his journey.

Answer 16

Ella le había dejado la cena en el horno por si él no hubiera comido nada durante el viaje.

Question 17

El Presente de Subjuntivo

Answer 17

is never used after por si/por si acaso.