Learn Italian: Questo muro impedisce che i vermi non entrino nel giardino. - This wall prevents the worms from entering the garden.

This is the pleonastic (extra) non which is the focus of this lesson. In Italian, verbs of hindering or preventing, like impedire, often take this extra non in the che clause. It doesn't actually negate the verb; instead, it emphasizes the negative event you are trying to stop. You simply leave it untranslated in English.

What would happen if I left the non out of this sentence?

If you wrote Questo muro impedisce che i vermi entrino..., the meaning would remain exactly the same! The pleonastic non after verbs of hindering is optional in modern Italian. Including it just adds a slightly more formal or literary tone to the sentence.

Why do we use the subjunctive entrino here instead of the indicative entrano?

The verb impedire (to prevent) expresses an action that tries to control or influence an outcome. Just like verbs of wishing, fearing, or commanding, it triggers the subjunctive mood in the dependent clause. Therefore, we use entrino, the present subjunctive of entrare.

Could I translate 'prevents the worms from entering' using an infinitive instead of a che clause?