Complex uncertainty expressions such as 'probably likely' and 'certainly possible' naturally occur in everyday conversations. However, they received much less attention in the literature than simple ones. We propose a probabilistic model of the use and interpretation of complex uncertainty expressions based on the assumption that their predominant function is to communicate factual information about the world, and that further layers of uncertainty are pragmatically inferred. We collected empirical data on the use and interpretation of these expressions and use it for detailed model criticism.