Midgley wrote her 2014 book, "Are you an illusion?" as a response to Francis Crick's argument in his book "The Astonishing Hypothesis" that a person's sense of personal identity and free will is no more than the behaviour of nerve cells. She attacks the understanding inherent in this argument that everything, including a sense of self, can be understood through its physical properties. Instead, she argues that there are different levels of explanation, which need to be studied using different methods. This means that thoughts and memories are an integral part of reality for both humans and animals and need to be studied as such.