Trust and trustworthiness are core social phenomena, at the heart of most everyday interactions. Yet they are also puzzling: while it matters to us that we place trust well, trusting people who will not let us down, both also seem to involve morally driven attitudes and behaviours. Confronted by whether I should trust another, this tension creates very practical dilemmas.

In Trust, Thomas Simpson addresses the foundational question, why should I trust? Philosophical treatments of trust have tended to focus on trying to identify what the attitude of trust consists in. Simpson argues that this approach is misguided, giving rise to merely linguistic debates about how the term 'trust' is used. Instead, he focuses attention on the ways that trust is valuable. The answer defended comprises two claims, which at first seem to be in tension. One is a form of evidentialism about trust: normally, your trust should be based on the evidence you have for someone's trustworthiness. But, second, someone's word is normally enough to settle for you whether you should trust them. Social norms of trustworthiness explain why both are normal.

Methodologically innovative, Trust also applies the account , addressing how cultures of trust can be sustained, and the implications of trust in God. While it is a philosophical essay, the book is written in a way that presumes no prior knowledge of philosophy, to be accessible to the scholars from the many disciplines also attracted and puzzled by trust.