Thought experiments are one of the most valued tools in philosophy. They have been used since ancient times, and still remain just as useful nowadays. Some of them may sound extravagant, but they are not daydreaming. This seems to be a misconception about philosophizing, possibly connected to the stereotype of a philosopher as a person removed from reality. However, under their seemingly idle, speculative nature, lies the key to reflection.
Thought experiments allow us to construct highly improbable, or even borderline impossible scenarios, all in order to probe an idea. Just like with normal experiments, they start with some assumptions and try to test how a claim will hold up when tested. Unlike lab experiments, they have an infinite budget and can be executed in precisely the way one desires, including having control over time.
The chief purpose of a thought experiment is not to gain data about the world, but to reflect on one’s ideas about the world. It turns out that when we try to verify our assumptions, a lot of them appear to not be as certain as we thought, giving us a chance to refine our understanding. In this way, thought experiments are checks on our ways of thinking.
But how do you get insight from just imagining things? Perhaps it’s best to refer to an example from another discipline – physics.
For a very long time in the West, Aristotle’s physics was considered to be the accurate description of the laws of nature. One of its postulates was that every physical body will eventually end up standing still, unless some force was to act upon it. This made intuitive sense – after all, stones rolled down a hill eventually stopped, and one couldn’t just push a cart and have it go forever.
But then came Galileo and with his thought experiment he questioned the notion that there’s something inherent about physical objects that makes them become still after some time. His method gave birth to the concept of inertia, and classical Newtonian mechanics that most people learn in school uses that exact concept to explain laws of motion. His experiment is a clear example why challenging and testing ideas is not just daydreaming. (And if Galileo’s physics seem too old-time, how about Einstein?)
Thought experiments in philosophy are similar, but unlike in physics they deal not with expressions of behaviour of the physical world, but rather the pure ideas that lie at the source of our understanding. They are not so much about the content, but the conclusions. So, we might wander about the nature of identity by asking about creating human replicas, or the right moral choices by wandering about killing a person to stop a trolley.
In the end, what we get is more than idle wandering – what we end up is an insight into how we think, and possibly how we should think.