Trust is as elusive in philosophy as it can be in practice. Philosophers often simply ignore or presuppose it, and when they do consider it, they often struggle to explain it or confuse it with other things. Nonetheless, by considering some major philosophers’ thoughts on trust and related matters, we can reveal certain important features of it, and see why it might be so elusive, in both philosophy and practice.

The ring of invisibility

In The Republic, Plato recounts a dialogue between Socrates and Glaucon, Plato’s older brother. In it, Glaucon argues that only the fear of detection and punishment prevents a human being from breaking the law and doing evil for the sake of his own self-interest. Glaucon thinks that this natural fact is demonstrated by the shepherd Gyges, who found a gold ring which made him invisible whenever he twisted it on his finger. (According to the story, he found the ring on a corpse in a hollow bronze horse, which was revealed when an earthquake opened up the ground beneath his flock.) On realising the ring’s power, Gyges used it to seduce the queen, murder the king, and take the throne. Glaucon’s claim then, is that every one of us, however law-abiding and good we might seem, would do as Gyges did, or something else in our self-interest, if we could avoid detection and punishment. And, Glaucon claims, we would be right to do so, since each human being’s only interest is their own self-interest, and we have no interest in justice and morality for their own sakes.

This sorry picture of human nature has been accepted by many philosophers since Glaucon, and, indeed, by many other people as well. It raises the following crucial question: when and why should we trust others, if we think that only the fear of detection and punishment prevents them from harming and stealing from us? Glaucon’s answer is that we should trust others only if we are confident that they fear detection and punishment sufficiently to dissuade them from harming or stealing from us. Thus I should trust the doctor to prescribe me appropriate treatment - and not, for example, make me the unknowing guinea pig for a new, untested medicine - only if I think that she is sufficiently afraid of being found out and struck off if she does not.

This seems reasonable, and reveals an important feature of trust: when we trust others, we are confidently relying on them to take care of something which we care about, but which they could harm or steal if they wished. When we trust then, we make ourselves vulnerable. But we do so in the confidence that the trusted will not exploit this vulnerability, and generally in the confidence that the trusted will actively take care of what we make vulnerable. This vulnerability and care can concern something tangible, such as when I trust my friend with my bike, or something less tangible, such as when I trust a stranger to be honest when I ask him the time.

But Glaucon’s answer...