At the heart of the arguments I shall present for the reality of human freedom and, indeed, of our distinctive agency, is what is called “intentionality”. Intentionality is a notion that has had a venerable history. It was there in ancient Greek and Islamic philosophy, and was important to Stoic and medieval philosophers. Since it was revived by the German philosopher Franz Brentano towards the end of the nineteenth century, intentionality has had a central presence in so-called continental philosophy and, in recent decades, in the analytical philosophy of mind. For philosophers “intentionality” may seem all-too-familiar and for non-philosophers technical and obscure. Notwithstanding the technicality of the term, it is something whose essential nature can be grasped by a moment's thought. Its apparent simplicity, however, is deceptive. Intentionality, like the concept of “the atom” in physics, has proved to be a gift that keeps on giving.

Intentionality is “the mark of the mental”. It is what distinguishes mental states or events such as perceptions, thoughts, beliefs, desires from other items in the world. It is “the power of minds to be about, to represent, or to stand for, things, properties, and states of affairs”.2 Importantly, these items are other than, and distinct from, those mental states. While intentionality is a fundamental and universal feature of mental states or entities, no physical entity has this feature. Physical events may be (or, as we shall see, may not be) causally related to other events but they are not about them.

How mental states relate to what they are about will vary according to the state in question. It will be different in perceptions, beliefs, knowledge, thoughts and desires. There is, however, something that they have in common and it is this, as we shall see, that accounts for the possibility of truly voluntary action. The relationships of “aboutness” between our mental states and the external world hold open a space between ourselves as conscious subjects and the world (or perhaps worlds) to which we relate as the theatre of our lives.