Bonjour Cécile:  Merci pour la reponse.  À partir de maintenant, je poserai ça là.  Au fait, j'aime beacoup de votre site.  Il m'a vraiment aidé.    Don

Bonjour Jennifer, While Aurélie does an excellent job in providing the pronunciation rule, I have located a couple of other sites that, perhaps, can give you some added insight: https://frenchmoments.eu/pronunciation-of-french-adverb-plus-when-to-sound-the-s/ https://www.youtube.com/watch?v=fvc6KpW7jfw https://www.youtube.com/watch?v=Uv7nTsxUy30 https://www.youtube.com/watch?v=UaA8pcL8LeQ https://www.thoughtco.com/learn-french-expressions-with-plus-4084866 I, too, have difficulty in remembering exactly when to pronounce the «-s». I hope you find these helpful. J'espère que ma réponse vous aiderait. Bonne chance et bonne continuation dans vos études en français, la langue de Molière et qui a été utilisé par le monde français depuis l’époque d’Hugues Capet

The grammatical answer is: when "plus" is used as a pronoun meaning "more" you pronounce the final s. When it means "less" or when it is used as part of a negation you don't pronounce the s (unless it is followed by a vowel). Plus de messages (with silent s) = no more messages Plus de messages (with s pronounced) = more messages In this case you can't devine the meaning unless you know the context or you hear it spoken. -- Chris (not a native speaker).

Thank you both for that. I will be checking out the sites you quoted Ron and Chris your answer reminds me why I find it so difficult to remember when to pronounce and when not.