Many West African languages, including Hausa and Fulfulde, have particles, traditionally called modal particles in Hausa, and modal constituants in Fulfulde, which may appear in topicalisation. These particles come to specify, from a semantic point of view, the nature of the topic. They are generally not translated in the examples that can be found in the dictionary, or, if they are, it is in the form of a generic "as to". The purpose of this paper is to identify the syntax and semantics of these particles. In doing so, we are led to specify what operations are at work in topicalisation and focusing. Indeed, the addition of particles reveals that topicalisation in Hausa and Fulfulde works in a way that is different from prototypical cases g...