It's All About Rank and Precedence

Reading Les Liaisons Dangereuses made me curious about something: who outranks whom in terms of titles? And what exactly is a chevalier? And what is the correspondence to the British nobility, a system I'm a little more familiar with. So I did some research and it's pretty interesting. 

The French nobility (la noblesse) was the privileged social class in France during the Middle Ages and the Early Modern period until the French Revolution in 1789. The nobility was revived in 1805 with limited rights as a titled elite class from the First Empire to the fall of the July Monarchy in 1848, when all privileges were abolished, and survived in hereditary titles until the Second Empire fell in 1870.

In the political system of pre-Revolutionary France, the nobility made up the Second Estate of the Estates General (with the Catholic clergy comprising the First Estate and the bourgeoisie and peasants in the Third Estate). Although membership in the noble class was mainly passed down though hereditary rights, it was not a closed order. New individuals were appointed to the nobility by the monarchy, or they could purchase rights and titles or join by marriage.

During the ancien régime, there was no distinction of rank by title (except for the title of duke, which was often associated with the strictly regulated privileges of the peerage, including precedence above other titled nobles). The hierarchy within the French nobility below peers was initially based on seniority; a count whose family had been noble since the 14th century was higher-ranked than a marquis whose title only dated to the 15th century. Precedence at the royal court was based on the family's ancienneté (seniority by age), its alliances (marriages), its hommages (dignities and offices held) and, lastly, its illustrations (record of deeds and achievements).

• Titles:
• Duc: (Latin dux, literally "leader") possessor of a duchy, was originally the governor of a province, usually a military leader. 
• Prince: possessor of a lordship styled a principality (principauté); most such titles were held by family tradition and were treated by the court as titres de courtoisie -- often borne by the eldest sons of the more important duke-peers. This title of prince is not to be confused with the rank of prince, borne by the princes du sang, the princes légitimés or the princes étrangers whose high precedence derived from their kinship to actual rulers.
• Marquis: possessor of a marquessate (marquisat), but often assumed by a noble family as a titre de courtoisie. In older times it was a count who was also the governor of a "march", a region at the boundaries of the kingdom that needed particular protection against foreign incursions (margrave in German, marchioness (female) in Britain).
• Comte: (Latin comes, literally "companion") possessor of a county (comté)  and was originally an appointee of the king governing a city and its immediate surroundings, or else a high-ranking official in the king's immediate entourage. In Britain the equivalent would be a count. 
• Vicomte: possessor of a viscounty (vicomté) or self-assumed. Originally he was the lieutenant of a count, either when the count was too busy to stay at home, or when the county was held by the king himself. Equivalent to the British title of viscount or viscountess.
• Baron:  (a later title) was originally a direct vassal of the king and owned a barony, or of a major feudal lord like a duke or a count. 
• Chevalier: an otherwise untitled nobleman who belonged to an order of chivalry, such as the Legion of Honor or the Order of Malta. In earlier days it was a rank for untitled members of very old noble families. 

Many of these titles eventually became hereditary and formalities and didn't require any particular skill. 

If you want to get a pretty exhaustive look at the history of French nobility, I refer you to this website, which has all kinds of fascinating detail.