We contrast two types of sentences with a preposed NP in French in a construction based HPSG grammar. They differ with respect to different grammatical aspects (syntax, semantics, pragmatics and phonology), which cluster uniquely into constructions. Both are colloquial, a reason why they have been recognized only recently (see Zribi-Hertz 1986, 1996, Sabio 1995, 2006). Accordingly, we rely for the data on spoken corpora (Corpaix, CFRP) as well as on our intuitions. Both constructions involve a partitioned semantics but this mode of composition is associated with different effects. One construction is characterized semantically: the preposed NP is the theme of a categorical proposition. The other construction is characterized pragmatically: it is associated with an independent declarative clause, a typical use of which is to signal a break in the interaction.