posted 20th March 2025
Think of experiments, and you probably think of chemistry or physics lessons. Test tubes and bunsen burners; scales and rulers. An experiment is a way of seeing if a theory (an idea supported by some evidence) or a hypothesis (an idea with no existing evidence) is true by testing it under controlled conditions. What temperature does water boil at? Heat up some water and put in a thermometer when it starts bubbling. It says 100 degrees. Do it a couple more times to check. It’s still 100 degrees. Right, that’s it, we’ve proved that water boils at 100 degrees.
For a thought experiment you don’t need test tubes or weighing scales. You just need your imagination. Thought experiments begin with a ‘what if …’. They involve imagining a scenario that doesn’t currently exist, and working out what the consequences would be if it did exist.
Most commonly the scenarios are either impossible, highly unlikely, or possible but unethical. Thought experiments shock you into looking at the world in a new way, and can often change your thinking. Changing their listeners’ thinking is exactly what debaters do, so thought experiments should be in their toolkit.
Here are some examples of different types of thought experiment, and ways in which they could be used in a debate.
1. Impossible
The veil of ignorance
The veil of ignorance is a very famous thought experiment invented by the philosopher John Rawls.
What if … before you were born, you were sitting up in heaven, looking down at the world as it is, knowing that you could be born into any family, anywhere? Would you want to keep the world as it is? If not, how would you change it?
This thought experiment challenges ideas such as equality of opportunity and meritocracy: the belief that everyone has an equal chance of success, and that it is fair to reward people for their achievements. Do you really believe that two equally intelligent babies, one born to a hedge fund manager in South Kensington (a rich area of London), and one born to unemployed parents in South Shields (a poor area in the north east of England), will have an equal chance of getting into Oxford? Do you really think a baby born into a black family is going to have exactly equal chances to a baby born into a white family?
If you were in the celestial waiting room, would you want to take the risk? Wouldn’t you want to make society more economically equal - make some people less rich, and others richer? Wouldn’t you want some interventions to correct structural racism? Wouldn’t you want to get rid of private schools and all the advantages they bring, given that you’d only have a 7% probability of being sent to one?
The veil of ignorance is a very powerful tool if you are arguing for measures such as increased taxes, higher public spending and more generous welfare provision, all of which reduce economic inequality; or for interventions to support underrepresented groups, such as quotas for education or employment; or against goods such as private education which promote privilege.
2. Highly unlikely
What if … there were no controls on immigration whatsoever, and anyone from any country could live and work in any other country?
This thought experiment makes us think hard about immigration and its consequences. You can take it either way; for or against controls on immigration.
If you are arguing for greater restrictions on immigration, you could paint a picture of utter chaos, with richer countries being swamped by people from poorer countries, causing their health and education systems to collapse, and use this as an argument for the importance of immigration controls.
If you are arguing for a more liberal immigration regime, you could argue that removing all controls would actually solve our immigration problems. People smugglers who cheat people out of their life savings and put them in leaky boats across the English Channel would go out of business overnight, as anyone who wanted to come to Britain could do so safely. We wouldn’t be swamped, as market forces would ensure people would only come if there were jobs for them. Once all the jobs were filled, they would go to another country.
3. Possible, but unethical
What if … disabled babies were all killed immediately after birth?
This would be physically possible (and has been practised in some societies), but most people would consider it morally unacceptable. However, it does force us into thinking more deeply about questions of life and death.
It is particularly relevant for debates about abortion and assisted dying. Currently, it is legal in the UK to abort babies with Down’s Syndrome up until the point of birth. Why? Why is it all right to kill them in the womb, but not a few hours later? If we can abort babies in the womb for being disabled, why should we keep them alive once they’re born? If assisted dying becomes legal in the UK, we will be able to help people who have a terminal illness to kill themselves. Why not do the same for people with a crippling disability which stops them from living a full life?
This thought experiment tends to support opposition to more liberal laws around abortion and assisted dying. It does so by pushing to a logical extreme some of the arguments in favour of these measures, and arriving at an unacceptable conclusion.
Thought experiments may look like fanciful games, but they can end up changing the world. Every adult being allowed to vote, regardless of wealth or gender; men marrying men and women marrying women; a machine in your pocket that allows you to see and talk to someone thousands of miles away - all these were once crazy thought experiments, but are now part of our daily lives.
