Doing thought experiments is one of the methods used in philosophy. Philosophers discuss often problems that need experimentation. However, in many cases this is no practical option. Many philosophical issues are related to man and society, and, for instance, one cannot force people to undergo brain surgery for the sake of answering philosophical questions. What remains then are analytical methods. Doing thought experiments is one of them.
Man’s imagination is boundless. Man can think almost everything. This applies also to thought experiments. However, does every experiment that we can think lead to valid results? In fact it is so that a though experiment, like every experiment, can produce such results only if its premises are true. This logical fact is largely ignored when discussing the results of thought experiments. For instance, in action theory there is a thought experiment in which a surgeon puts something in a brain which make it possible to manipulate the agent’s movements. But what value do conclusions based on this thought experiment have if we do not know whether such an operation is basically possible? Even more, the argumentations about personal identity in the analytical philosophy are founded mainly on thought experiments of dubious value. Brains are switched between persons. Brains are split and the parts are placed in the heads of different persons. People are scanned and teletransported to other planets. On the basis of such thought experiments philosophers come to far-reaching conclusions about our personal identity. However, what is never done in the discussions about personal identity is questioning whether brain switches and teletransport are fundamentally possible at all. I think that in the light of the present research and literature on the relation between the brain and the rest of the body and between mind and body these thought experiments are not possible, for the working of the brain is based on the working of the body, at least for a part. Moreover, a part of what we essentially are is just in our body. If we suppose then in a thought experiment that our brain and body are separated, the conclusion that the brain – and the mind, which is supposed to have its residence in the brain – carries our personality and that the essence of what we are is our psychology is actually a repetition of the main premise of our thought experiment. We suppose that we can separate brain and body, so we can come to no other conclusion then that we fundamentally are our brain (or mind). In other words, it is begging the question.
Thought experiments can lead to valid conclusions only if we can make true that their premises are realistic. As long as we do not try to substantiate that a certain thought experiment represents a fundamentally possible event, it is a doubtful instrument. However, this is often disregarded by philosophers who study personal identity.