It has become popular of late to identify the phenomenon of thinking a singular thought with that of thinking with a mental file. Proponents of the mental files conception of singular thought claim that one thinks a singular thought about an object o iff one employs a mental file to think about o. I argue that this is false by arguing that there are what I call descriptive mental files, so some file-based thought is not singular thought. Descriptive mental files are mental files for which descriptive information plays four roles: determines which object the file is about, if any, it sets limits on possible mistakes that fall within the scope of successful reference for the file, it acts as a ‘gatekeeper’ for the file, and it determines persistence conditions for the file. Contrary to popular assumption, a description playing these roles is consistent with the file-theoretic framework. Recognising this allows us to distinguish the notion of singular thought from that of file-thinking and better understand the nature and role of both.