ne explétif with 'avoir peur que'

Question

I've answered the quiz question: "J'ai peur qu'ils _________ la vérité." with "ne sachent." This was marked incorrect and the correct answer was "sachent." I submitted that as an error, but the response there was to come here and ask why it's incorrect.

I've reviewed the 'ne explétif' lesson over and over and am sure I've lost my mind. In that lesson, "avoir peur que" is NOT marked as depending on whether the phrase is negative and says that it always takes the 'ne'. Can anyone help me understand why my answer is incorrect? Many, many thanks.

Accepted Answer

Hi Molly,
I understand your frustration as the ‘ne explétif’ is not easy.
In my opinion you should have the ‘ne’ in written form but it would be dropped in speech.
However, if you say -
J’ai peur qu’ils sachent la vérité
It eliminates the doubt completely and your fear that they may know the truth becomes almost a certainty. 
I will however try and get someone to have a look at this to see if it is an error indeed.
In the meantime , hope this helps!

Answer

Bonjour Molly !Indeed, here you were correct to insert the "ne" explétif, though it isn't compulsory, as Cécile explained. As this was a conjugation question, we didn't think of including the option of adding the "ne", but it is of course correct here, so thanks to your feedback, we've now marked it as correct :)Merci encore et bonne journée !