Let’s talk about Joe and Josh. Both are 15-year-old teenage boys, but unfortunately, their childhood years have been plagued by countless surgeries and hospital visits. Both have rare cases of cystic fibrosis, and it is unlikely that their conditions will be cured in the near future—both will continue to lead lives of pain and struggle. Yet, although both struggle to do actions that would be extremely easy for some of their classmates, they still find joy in their lives. Lucky enough to have each other, Joe and Josh both enjoy philosophy, playing video games, working out when they can, and commiserating about their lives. Despite the overwhelming pain they endure, both of them would be the first to admit that their lives are undoubtedly worth living.

Let’s zoom back 15 years into the past, where a shocking truth is revealed. Due to an elaborate (and illogical) attempt at insurance fraud, both Joe’s and Josh’s parents attempted to give their kids cystic fibrosis, hoping that they would be able to get more money to support their struggling families. What evil parents! However, they tried to give their kids the disease in different ways. Joe’s mom sees an evil doctor to manually select the only sperm that carries the cystic fibrosis trait, which they decide to fertilize. Josh’s mom, on the other hand, takes a handful of pills midway through her pregnancy in order to give her baby a disease (this may make no sense biologically, but that’s not the point).

As we can see, both parents are successful in their attempts to give their sweet young babies cystic fibrosis, ensuring that both of them grow up in a world of pain. Fortunately, their attempts at insurance fraud fail, but unfortunately, now that they have no money, Josh and Joe grow up in broken households. So despicable!

However, well-known philosopher Derek Parfit decrees that only one of the children is actually harmed, although both mothers are terrible people. This is the root of the non-identity problem, which challenges our intuitive assignments of blame. Can you guess who is harmed—Joe or Josh (according to Parfit)?

Before I reveal the answer, let’s go through a quick definition of what harm is, at least to philosophers. While many of us may think harm is just a bad thing happening to someone, philosopher’s would argue that to be harmed is to be made worse off than you otherwise would have been. For example, if you give someone a black eye, we can unquestionably say they were harmed, as they are worse off (bruises, headache, embarrassment, explaining to parents) than they were before the punch.

Let’s start with Joe’s mom, who went to the evil doctor. Remember, the evil doctor, using his super-advanced, futuristic, and unethical technology, selected the exact sperm cell that carried the trait that eventually gave Joe cystic fibrosis. He did this purposely, and quite effectively, as it worked. But here’s the kicker: even though Joe lives a life of pain, he still agrees that he has a “life worth living.” And if his mom had never gone to the evil doctor, and never selected the sperm with the cystic fibrosis gene, he never would have existed in the first place. This is the core of the non-identity paradox: as the only other option for Joe is non-existence, however pitiful his life is, he could not have been harmed, if we use the strict philosophical definition. As harm would require someone to be “made worse off than they would have been otherwise,” and Joe quite literally “could not have been otherwise,” as he would not have existed, then he was not really harmed.

On the other hand, Josh could have been different. The thought experiment was constructed in a way to illustrate this difference. As Josh’s mom took the cystic fibrosis-inducing pills in the middle of her pregnancy, Josh could plausibly have been otherwise, i.e., without cystic fibrosis—if only his mom hadn’t taken those pills. So, in this scenario, while both parents are horrible people, only one of their children—Josh—was actually harmed, in a strict philosophical sense.

The non-identity problem has profound implications. It challenges our intuition about what is perceived as harmful, and what unethical actions really are. It also applies to pollution and future generations: suppose we have two options, either polluting the world or not. If we choose to pollute the world, our future children may live in an environment with persistent flooding and heat waves, but at least they exist. If we decided not to pollute, it’s likely that due to the randomness of life and the “butterfly effect,” the same person wouldn’t have been born. So again, even though their life on the polluted earth is miserable, their only other option would be non-existence—which they can agree would be worse.

I’d like to end this article by revealing the standardized non-identity problem argument. Here it is:

• An action only harms a person if they would have been better off in some way.
• In many reproductive cases, the identity (and existence) of the person depends on the action taken.
• If an action determines one’s existence, there would be no scenario where the same person would have been better off.
• A life is always worth living.

Conclusion 1: The person who was born, albeit into a world of pain, was not actually harmed.

Conclusion 2 (the paradox): Either we reject (a) our intuition, stating that, for example, polluting the planet or selecting for a child with cystic fibrosis is not wrong, or (b) challenge the standard philosophical definition of harm.