We attribute the capability of imagination to the madman as to the scientist, to the novelist as to the metaphysician, and last but not least to ourselves. The same, apparently, holds for thought experimentation. Ernst Mach was the first to draw an explicit link between these two mental acts; moreover - in his perspective - imagination plays a pivotal role in thought experimentation. Nonetheless, it is not clear what kind of imagination emerges from Mach's writings. Indeed, heated debates among cognitive scientists and philosophers turn on the key distinction between sensory and cognitive imagination. Generally speaking, we can say that sensory imagination shares some processes with perception, cognitive imagination with the formation of belief. Both the vocabulary used in the literature on thought experiments and what I refer to as "Machian tradition" indicate imagination as a notion of central importance in the reasoning involved in thought experiments. However, most authors have really focused on sensory (in particular, visual) imagination, but have neglected the second kind. Moreover, some authors attribute to Mach the idea that it is visual imagery that is primarily at work in thought experiments. I claim another interpretation is possible, according to which Mach can be said to deal with cognitive imagination. The main aim of this paper is to retrace Mach's original arguments and establish a connection with the cognitive literature on imagination. I will argue that imagination tout court could play a role in thought experimentation. Once imagination is seen as the key to the "cognitive black-box" of the thought experiment, we will have moved a step closer to a simulative imagining-based account of thought experimentation.