1. Literary/refined - Littéraire/soutenu
Literary French is extremely formal and elegant language which is nearly always written. When spoken, it tends to be for effect and sounds snobbish or old-fashioned. Poetic French is a subcategory.
2. Formal - Formel
Formal French is polite language, both written and spoken. It is used when the speaker doesn't know, wishes to show respect for, or wants to demonstrate distance/coldness toward another person.
3. Normal - Normal
The normal register is the largest and most common category of language, what you might call everyday language. Normal French has no particular distinction (neither formal nor informal) and is the language used by and between just about everyone. It includes various subcategories of specialized and technical language, such as administrative, judicial, and scientific jargons.
4. Informal - Familier
Informal French expresses closeness and is typically used between friends and family. Baby talk and most apocopes are informal. Although informal French is grammatically correct, it is at the bottom end of what the French call bon usage (correct usage).
5. Familiar - Populaire
Familiar French is used between friends and expresses closeness verging on disrespect. Verlan and largonji are subcategories, though their individual words can range from normal register to slang.
6. Slang (vulgar) - Argot (vulgaire)
Slang is vulgar, offensive, and usually insulting language, often related to sex, drugs, or violence. It may be used between friends or enemies. The familiar and vulgar registers are considered non-standard French.
The following aspects of French have variations according to the register of French being spoken/written.
- Gestures
Gestures range from normal to vulgar.
Grammar
* literary tenses
* negation
- formal negation
- informal negation
* pronouns
- ceci, cela, ça
- informal pronouns
- nous vs on
- tu vs vous
* questions
- informal questions
Pronunciation
* e muet
* informal pronunciation
* liaisons
Vocabulary
* apocopes
* baby talk
* expressions
* largonji
* slang
* verlan

