Epistemological optimists about thought experiments hold that imagination could be under certain conditions source of epistemic justification. Their claim is usually based on one of three dominant conceptions about epistemic value of thought experiments. Apriorism states that imagination may serve as unique a priori source of new synthetic knowledge about the actual world. I argue against this view and show that apriorism is either too weak, or too strong or too vague. Psychologism is viable, yet not fully clear conception about (...) new meta-knowledge obtained by thought experimenting. I compare some interpretations of this position and present reasons for favorizing one of them. Conceptualism considers thought experiments as instruments for cleaning our conceptual systems. I argue that this position is in fact not about epistemic value of thought experiments, but about one specific usage of experimental result. (shrink)