One of the many questions that have been asked about thought experiments is the ontological question concerning what thought experiments are, and specifically, if they are some sort of experiments – perhaps experiments with specific characteristics, but experiments nonetheless. The ontological question of what thought experiments are is entangled with the epistemological question of understanding where the knowledge that they bring may come from and what kind of knowledge exactly they can bring. Without dissociating the ontological question and the epistemological question, this chapter defends a dialectical account of thought experiments. It characterizes thought experiments and insists on the heterogeneity between propositional and non-propositional knowledge that such a characterization implies. The chapter interprets the epistemological debate between James Robert Brown and John Norton in terms of this ontological unstable equilibrium, which would clarify their position in this debate. It argues for the acquisition of knowledge that is at stake in thought experimenting, one should propose a dialectical account of argumentation.