There is something very strange about conscious experience. It appears to be private and not accessible to anyone else, and yet it is the only aspect of my mental life that I can report to others. And why do I need any conscious experience at all when I can achieve so much without it? Thomas Huxley believed that consciousness was an epiphenomenon and ‘as completely without any power of modifying that working [of the body] as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery’. I shall argue that conscious is indeed like the steam whistle of a locomotive engine, in that it has a critical role in regulating interactions with other people.

Consciousness is a biological process that has evolved. Humans have much richer conscious experience than other animals and I believe that this gives us advantages. But what are these advantages? A great deal can be achieved without conscious experience including sensory integration, global information access, and flexible decision-making. But only through consciousness can we share our experiences with other people. Such sharing enables us to be influenced by the ideas of others and allows us to influence them. Such sharing creates advantages at many levels.

Consider, for example, the experience of action. Although our access to the cognitive processes underlying our actions is very limited we devote much time to justifying these actions to each other. Such discussions usually concern the experience of agency. This experience has little impact on our immediate behaviour, but we have a vivid experience of being in control: it is I that am performing the action, and I could have done otherwise. The feeling that I could and should have done something else creates the strong emotion of regret 

In the long run discussions about our experiences of action lead to cultural consensus about when we can be held responsible for our actions. We distinguish between outcomes that were the consequence of deliberate, free actions and those that occurred accidentally. In most cultures punishment for bad behaviour depends upon degree of responsibility. Such punishment has a key role in maintaining social cohesion. The regret we feel when we violate social norms is an internalised form of such punishment. Consciousness, reportable subjective experience, enables the development of cultural consensus and allows the group to achieve more than its best individuals.