Intentionality is 'aboutness': words, pictures, signs, beliefs, desire, and, indeed, intentions are all about things. The use of the word in this sense goes back to the Middle Ages, and Thomas Aquinas in particular; the topic was revived by Brentano, who thought that intentionality was so obviously inexplicable in physical terms that it proved the existence of a non-material world. But although intentionality is hard to explain, it isn't really an esoteric matter. Indeed, one of the things which make it difficult to deal with is its very familiarity; our normal life is so saturated with meanings and intentions and interpretations that we find it difficult to step back far enough to focus on the subject. There is also, as a result, a constant danger of including words or ideas which presuppose intentionality in the theories which are meant to explain it.
A mere study of terminology, even when done correctly, tracks the wrong items. Over the course of their history, technical terms are often used to express very different concepts: consider the terms 'substance,' 'matter,' or even 'concept.' Conversely, a single concept is often expressed by different terms, some of which may not be technical ones at all - a situation especially likely at the beginning of inquiry into the subject. So even when terminology is used as evidence, more must be brought into consideration. Philosophical interest should focus on the concept of intentionality itself or, better still, the divergent conceptions of intentionality that philosophers have had, and their resulting disagreements. These differences afford us the greatest perspective on our own presuppositions and preoccupations.
The best way to approach this is by looking at the history of the problem of intentionality: the difficulty, that is, of providing a philosophically adequate account of the nature of intentionality, in light of its various peculiarities (whatever terms may have been used to refer to it). Such an approach not only allows room for different theories of intentionality, but also includes attempts to dissolve the problem, either by dismissing the phenomenon entirely or by denying that there is any genuine difficulty involved.
