Subjunctive - impersonal phrases

Question

Is the subjunctive used after negative impersonal expressions?

For example: It is possilbe she may go. is "Es posible que ella vaya." But is it also subjunctive for It is not possible she may not go. ? Can you tell me the rule that applies here?

Answer 1

There are verbs like creer that use the indicative when positive and the subjunctive when negative, but usually it depends on what the statement is expressing: opinion, doubt, emotion, possibility, etc. or certainty, truth, 100% probability, etc.

This site lists a lot of the common impersonal expressions:

Notice that "Es imposible que...requires the subjunctive. That phrase would be the same as "It is not possible that...". Reason? You are expressing an opinion or a possibility.

Even a sentence like "It is impossible for two objects to occupy the same space at the time" isn't stating a fact, but a 0% probability.

Impersonal statements that suggest 100% probability such as "es cierto que", "es verdad que", "es evidente que" use the indicative.

Note: I think that espérar listed on that site is a typo (esperar)

Answer 2

Welcome to the forum!

This is a general rule of thumb, but it's easy to remember and if the subjunctive is new to you, this might help you out.

If the expression means that something is: true, certain, clear, evident, obvious, beyond the shadow of a doubt -the next clause is in the indicative.

Other impersonal expressions are followed by a clause in the subjunctive.

Remember: this is a general rule of thumb and it is very helpful to people who are starting to learn the subjunctive.

To answer your specific question: Both "it is possible" and "it is not possible" are followed by the subjunctive since neither one of them is synonymous with"it is true/certain/clear/evident/obvious", etc.

I hope that this has helped.