Loyalty is a broader concept than trust. Loyalty can be based on trust, typically long-standing trust, but can also be based on other things. Thus, loyalty to one’s country or football team, or to a tyrant, is based on something quite other than trust. Certain pets may offer the illusion of trust, but more properly offer loyalty.

The word ‘loyal’ is related to the word ‘legal’ and has, or had, feudal connotations, akin to ‘allegiance’ but with more feeling or personal involvement. Still today, loyalty is often to something that is greater than or beyond us. To call someone loyal can be slightly demeaning, whereas to call someone trustworthy is invariably ennobling.

Trust may be associated with love, and, especially with romantic love, can be a prerequisite for love. But it is entirely possible to love someone, and even to rely on his love, without also trusting him—as we often do, for example, with children. Conversely, we often trust people, such as doctors and judges, who do not love or even sympathize with us.

We can rely on someone to be a certain way or do certain things, such as turn up on time, get angry, or lose our keys. But trust is more than mere reliability, or, as we have seen, mere loyalty. Instead, trust is established when I ask or allow a suitable candidate to take at least some responsibility for something that I value, thereby making myself vulnerable to her, and she agrees to take that responsibility, or, in the circumstances, can reasonably be expected to do so.

I trust my doctor with my health because, by virtue of being a doctor, and my doctor, she has taken some responsibility for my health—and, of course, I have asked or allowed her to do so. But even then, my trust in my doctor is not all-embracing: given the kind of person that she is, and the nature of our compact, I can trust her with my health, but not, say, with my housekeeping or my finances.

My doctor may well one day decide, for one reason or another, to stop caring for my health, but I would expect her to regretfully make me aware of this fact, and maybe to make transitional arrangements so as to protect the thing that I value and entrusted her with, in this case, my health. If she withdrew herself in this measured and considerate manner, I would feel sad, disappointed, and perhaps annoyed, but I would not feel betrayed or let down, or, at least, not nearly as much as I would otherwise have.

The French for trust is confiance, which, like the English ‘confidence’, literally means ‘with faith’. Perhaps we cannot trust people not to let us down, other than by a leap of faith similar to belief in God, with the length of the leap determined by such factors as fear, habit, nature, reason, and love. But we can just about trust them—or some of them—not to mislead us, and to let us down lightly.