Les prépositions forment-elles une classe?

Although a large amount of work has been done in the last two decades on French prepositions, there is still no general agreement about their definition. One first has to make a decision about the necessity of such a class, a decision which can be based on the impossibility of accounting for various syntactic constraints without referring to the notion of "preposition". The main problem in trying to define that class seems to be that most of the 40-50 words generally listed as (simple) prepositions in French grammars have some semantic content, a fact that makes it possible to consider them as subordinating connectors, while only a few, primarily de and à, have no discernible meaning in various contexts, and do not necessarily play any linking or subordinating role. The various factors, semantic, lexical, syntactic or lexico-syntactic, which can trigger the occurrence of a preposition, make it difficult if not impossible to find some feature common to all the words traditionnally called prepositions in French.