According to Franz Brentano, intentionality refers to the "aboutness of mental states that cannot be a physical relation between a mental state and what it is about (its object) because in a physical relation each of the relata must exist whereas the objects of mental states might not."
Several problems arise for features of intentionality, which are unusual for materialistic relations. Representation is unique. When 'x represents y' is true, it is not the same as other relations between things, like when 'x is next to y' or when 'x caused y' or when 'x met y', etc. Representation is different because, for instance, when 'x represents y' is true, y need not exist. This isn't true when say 'x is the square root of y' or 'x caused y' or 'x is next to y'. Similarly, when 'x represents y' is true, 'x represents z' can still be false, even when y = z. Intentionality encompasses relations that are both physical and mental. In this case, "Billy can love Santa and Jane can search for unicorns even if Santa does not exist and there are no unicorns."
History
Franz Brentano, the nineteenth century philosopher, spoke of mental states as involving presentations of the objects of our thoughts. This idea encompasses his belief that one cannot desire something unless they actually have a representation of it in their minds.
Dennis Stampe was one of the first philosophers in modern times to suggest a theory of content according to which content is a matter of reliable causes.
Fred Dretskes book, Knowledge and the Flow of Information (1981), was a major influence on the development of informational theories, and although the theory developed there is not a teleological theory, Dretske (1986, 1988, 1991) later produced an informational version of teleosemantics. He begins with a concept of carrying information that he calls "indicating", explains that indicating is not equivalent to representing, and then suggests that a representation's content is what it has the function of indicating
Related theories
Teleosemantics, also known as biosemantics, is used to refer to the class of theories of mental content that use a teleological notion of function. Teleosemantics is best understood as a general strategy for underwriting the normative nature of content, rather than any particular theory. What all teleological theories have in common is the idea that semantic norms are ultimately derivable from functional norms.
Attempts to naturalize semantics began in the late 1970s. Many attempts were and still are being made to bring natural-physical explanations to bear on minds and, specifically, to the question of how minds acquire content. This is an interesting question; it is no surprise that it takes center stage in the philosophy of mind. Indeed, it is certainly an interesting question how minds, thought by those in the natural camp to be "natural physical objects", could have developed intentional properties. In the mid-1980s, with the works of Ruth Millikan and David Papineau (Language, Thought, and Other Biological Categories and "Representation and Explanation", respectively), teleosemantics, a theory of mental content that attempts to address the question of content and intentionality of minds, was born.
Ruth Millikan is perhaps the most vocal supporter of the teleosemantic program. Millikan's view differs from other teleosemantic views in myriad ways, but perhaps its most unusual characteristic is its distinction between the mechanisms that produce mental representations from those that consume mental representations. There is a representational function as a whole, at a composite level; and there are two "sub-functions", the producer-function and the consumer-function. In terms that are easy to understand, let's take Millikan's own example of beavers splashing their tails. One beaver alerts other beavers to the presence of danger by splashing its tail on the surface of water. The splashing of the tail tells, or represents to, the other beavers that there is danger in the environment, and the other beavers dip into the water to avoid the danger. The splashing of the beaver's tail produces a representation; the other beavers consume the representation. The representation that the beavers consume guides their behavior in ways that relate to their survival.