Intentionality

Intentionality refers to "aboutness." In classical cognitive science, intentionality is viewed as a property of mental representations: cognitive agents have beliefs, knowledge, hopes, dreams, desires, etc. about things. Whenever we come across "that" in an utterance or piece of writing, we know that we are dealing with something intentional. (Notice the intentionality of the preceding statement.) Brentano (1874/1995) argued that intentionality is a property that separates the psychological from the physical, and this general view is tacitly accepted by much of cognitive science.

This issue is important to the extent that any theory of consciousness, or mind, must answer as to how intentionality is possible. The notion of intentionality is critical in theories of folk psychology: when we predict the behavior of others by assuming that they are rational beings with beliefs, desires, and goals about the world, we are adopting what is known as the intentional stance

'Intentional' is not to be confused with 'intensional' spelled with an 's', the latter of which refers to the meaning of a term, (along with 'extensional'). Intentional, intensional, and extensional can be paired loosely in the following way: intentional/propositional, intensional/conceptual, and extensional/perceptual.

References:

1. Brentano, F. C. (1874/1995). Psychology From An Empirical Standpoint (Paperback ed.). London ; New York: Routledge.
2. Dennett, D. C. (1987). The Intentional Stance. Cambridge, MA: MIT Press.

(Added March 2010)