Por si acaso

Question

I don't see how you know from the 'in case you forget' sentence whether it is likely or not. Surely it depends on whom you are talking to?

e.g. my daughter, not likely to forget; my husband, very likely to forget. How can I tell from the question?

Silvia Píriz · Accepted Answer

Hola Jill T.
Great question! In Spanish, "por si acaso" (or just "por si") can be used regardless of the likelihood of an event happening—it expresses precaution rather than probability.
You're right that context matters, but in general:
1. If something is unlikely, "por si acaso" can be translated as 'just in case' (e.g., Llévate un paraguas por si acaso llueve → 'Take an umbrella just in case it rains').
2. If something is likely, "por si" can still be used, but it often implies the speaker expects it might happen (e.g., Te dejo una nota por si llegas tarde → 'I'll leave you a note in case you arrive late').
Unlike English, Spanish doesn’t explicitly differentiate whether an event is likely or unlikely—"por si acaso" always works as a precautionary measure. So, whether you say it to your husband or daughter, it doesn’t change the structure of the sentence—just the pragmatic implication in the conversation.
Hope this helps!
Saludos
Silvia

Silvia Píriz · Answer

Hola Scott O.
Jill is absolutely right that por si (acaso) is not about probability but about precaution, and that’s the key principle we aim to teach. However, you also raise a valid observation: in real-life communication, speakers may interpret the likelihood of an event differently and that can influence whether they choose indicative or subjunctive.
In practice, Spanish tends to follow a general pattern:

Indicative is commonly used when the speaker sees the situation as more concrete or plausible.

Subjunctive is used when the situation is more hypothetical, uncertain or less expected.

That said, this distinction is not always rigid, and there are indeed contexts where both forms could sound natural depending on the speaker’s perspective or intention. This can make it feel subjective from a learner’s point of view.
For the purposes of Kwiziq exercises, we sometimes need to guide learners toward the most typical or standard answer for a given context, even if alternatives might exist in broader usage. That said, your feedback is very helpful and we will review this type of question to ensure that acceptable variations are included where appropriate.
Thanks again for raising this, it’s exactly the kind of discussion that helps improve both the explanations and the learning experience.
Saludos
Silvia

Scott Oliver · Answer

Silvia has missed the point. The point is that some people are more likely to forget than others. With those people we would use indicative, and with the others we would use subjunctive, for the same precaution. This "likelihood" concept is subjective, and many of your exercises ought to allow either one to be used, but they don't.

This is similar to the one about making a big lasagna in case a couple of people come. Maybe it's unlikely that they'll come, but the speaker has the intention of freezing the uneaten portion, and will use the subjunctive. But only the indicative is accepted.