During conversational information retrieval, a user engages in a dialogue interaction with a search system in order to satisfy an information need. A profound understanding of the way in which users formulate and reformulate messages during this dialogue interaction, will aid the development and optimization of conversational search systems. This research analyses what query reformulation types are frequently used, and looks at how this differs between fact finding and information gathering search tasks. Existing research on query reformulation mainly focuses on traditional IR systems. The little research that has been conducted in a conversational context is based on interactions between humans, rather than incorporating a search engine. We are interested in conversational query reformulation in a text-based interface, using a web-based search engine. To this end, preliminary insights of an empirical user study are presented. On the basis of its results, a taxonomy of query reformulation types is defined. Additionally, significant differences are found between how fact finding and information gathering messages reformulate queries. These results contribute to a better understanding of the conversational search dialogue, which aids the further research and development of conversational search systems.