The directedness or ‘aboutness’ of many, if not all, conscious states. The term was used by the scholastics, but revived in the 19th century by Brentano. Our beliefs, thoughts, wishes, dreams, and desires are about things. Equally the words we use to express these beliefs and other mental states are about things. The problem of intentionality is that of understanding the relation obtaining between a mental state, or its expression, and the things it is about. A number of peculiarities attend this relation. First, if I am in some relation to a chair, for instance by sitting on it, then both it and I must exist. But while mostly one thinks about things that exist, sometimes (although this way of putting it has its problems) one has beliefs, hopes, and fears about things that do not, as when the child expects Santa Claus, and the adult fears Zeus. Secondly, if I sit on the chair, and the chair is the oldest antique in London, then I sit on the oldest antique in London. But if I plan to avoid the mad axeman, and the mad axeman is in fact my friendly postman, I do not therefore plan to avoid my friendly postman (see also extensional/intensional, referentially opaque/transparent). Intentional relations seem to depend on how the object is specified, or as Frege put it, on the mode of presentation of the object. This makes them quite unlike the relations whose logic we can understand by means of the predicate calculus, and this peculiarity has led some philosophers, notably Quine, to declare them unfit for use in serious science (see also eliminativism). More widespread is the view that since the concept is indispensable, we must either declare serious science unable to deal with the central feature of the mind, or explain how serious science may include intentionality. One approach is to suggest that while the linguistic forms in which we communicate fears and beliefs have a two-faced aspect, involving both the objects referred to, and the mode of presentation under which they are thought of, we can see the mind as essentially directed onto existent things, and extensionally related to them. Intentionality then becomes a feature of language, rather than a metaphysical or ontological peculiarity of the mental world.