-ness... where's the pattern in French?
In English, we have some words like happiness, sadness, randomness, laziness, tidiness, weakness etc... we can add -ness to turn such adjectives into nouns. Of course we have some irregularities, but in general we can follow this rule. It's often used even to make up new words. It's also a way for non-natives to make themselves understood, even if their usage it is not necessarily correct. However, in French I have not found any common pattern and it's making it really difficult to ask ''how \adjective/'' questions, because in most cases I don't know the word I need.
-esse and -eur seem to be closest... hauteur, longeur, largeur, profondeur, lourdeur, chaleur, vitesse, faiblesse, justesse, tristesse, paresse etc... but is there any way to make a good guess or even create a new, as easily as we can in English?
If I don't know the word, what would be my best guess? In English, we turn adjectives (sad) into abstract nouns (sadness) by adding -ness, and it works for a large percentage of adjectives. How can I do the same in French? Or do I have no choice but to learn all and memorize?
Well, it's not like it's a crime. But if the modified word doesn't exist and the properly modified word exists, it will feel weird.
In some cases, it is more or less tolerated as it is useful to do that kind of convertion even if it isn't proper.
That being said, while in English the transformation in -hood and -ness are rather obvious, in French those transformations are often much less obvious.
Voici quelques années une ministre française (ex-candidate à la présidence de la république) avait un peu attiré les moqueries en utilisant le mot "bravitude" lors d'un voyage en Chine. (brave / bravitude... hélas, en français on possède déjà bravoure, mais le mot a eu du succès et a été amplement commenté et repris parfois avec ironie et parfois non, et les humoristes ont joué à créer des mots en "itude" par dérision)
The problem in learning another language is that the logical is different. Because people is different, culture too. In fact, it is not a real problem, it's what we call diversity. That's make our planet so rich. Learning another language is like travelling : it is a way to discover another pattern of thinking, new believes...