Many physiologists have assumed the breath-lung theory, according to which respiration is a complex of lung processes. We will show, however, that breathing is extended, embodied, embedded, and enactive, and therefore should not be identified with lung functioning.

Consider Otto, a man with severe emphysema resulting from years of that destroyed the air sacs in his lungs. Gasping for breath, he is taken to a hospital where he is put on a medical ventilator that mechanically blows air into his windpipe through a tube. Otto is then able to breath, which shows that breathing is not just a lung process, but can be extended into the world by machines such as ventilators. Other breathing extensions include scuba gear for diving and continuous positive airway pressure machines used by people with .

Breathing is also embedded in the world and extended into it by virtue of the biological need for oxygen in the air that is external to a human. Accessing this air cannot be done just by the lungs alone, but requires a much larger physical system, including the mouth, nose, windpipe, and heart and circulatory system. Breathing is also to some extent under the conscious control of the brain. Hence breathing is fully embodied rather than just a lung process. Because the purpose of breathing is to enable the body to perform actions, it is appropriate to describe breathing as enactive as well as extended, embedded, and embodied.

Astute readers will notice the parallels between our extended breath hypothesis and the familiar extended mind hypothesis defended by philosophers such as Andy Clark and David Chalmers. Similar ideas about thinking being embedded, embodied and enactive have been defended by other philosophers such as Alva Nöe, Paul Thompson, and Anthony Chemero. We heartily endorse this exciting new approach to cognitive science, and look forward to future developments in theories of other bodily functions such as digestion and sexual reproduction, all of which extend into the world in ways too indelicate to report here.

Critics will undoubtedly complain that the extended breath hypothesis uses obvious observations about machines and interactions to obscure the fact that lungs are in fact the key organs for performing respiration. However, we think that our Otto thought experiment shows that the importance of lung mechanisms to breathing has been exaggerated, and physiologists will do better to pay to the entire system that includes the world and the body.

We take our inspiration from the German philosopher Heidegger who emphasized being-in-the-world over traditional views of humans as disembodied. Rather than dismissing Heidegger as obscurantist and antagonistic to science and technology, we have shown the benefits of applying his ideas to develop insights about breathing-in-the-world.