The phrase theory of mind can be used in several ways.

There are general categories of theories of mind.
There are the specific theories of mind attributable to individuals. In recent years, the phrase "Theory of mind" has commonly been used (following the paper "Does the chimpanzee have a theory of mind?" by David Premack and G. Woodruff, 1978) to refer to a specific cognitive capacity: the ability to understand that others have beliefs, desires and intentions that are different from one's own.

General categories of theories of mind:

In functionalist theories, functionalists like Georges Rey explore computational theories of mind that are independent of the physical instantiation of any particular mind.In brain-mind identity theories, biologists like Gerald Edelman are concerned with the details of how brain activity produces mind and work within the confines of the identity theory of mind

Theories of mind attributable to individuals:

We can also talk about theories of mind produced by individuals, such as Brentano's theory of mind. Georges Rey and Gerald Edelman were mentioned above as examples of people who deal with different broad categories of theories of mind within which they have each produced their own personal theories of mind.

"Theory of Mind" - Understanding that others have minds, with separate beliefs, desires and intentions

As the title of Premack and Woodruff's 1978 article indicates, it is also important to ask if other animals besides humans have a genetic endowment and social environment that allows them to acquire a theory of mind in the same way that human children do. This is a contentious issue because of the problem of inferring from animal behavior the existence of particular thoughts. Each of us knows by introspection that we understand that others have beliefs, desires and intentions that are different from our own and we infer that all humans with normal minds share this cognitive ability. Researchers who have spent a great deal of time with non-human apes tend to accept the likelihood that other apes like chimps also have a theory of mind. For example, Sue Savage-Rumbaugh takes this position in her book "Kanzi". Others such as C. M. Heyes take the position that we need not infer that chimps in the wild have any understanding of the mental states of other chimps.

There is interest in the idea that certain learned behaviors such as human language behavior, facilitate the development of a theory of mind in both humans and chimps. In the context of language users, Sue Savage-Rumbaugh (Kanzi, page 272) has described "theory of mind" as the idea that "knowledge states of the speaker and the listener can in fact be different."

There has also been speculation that certain humans fail to progress through the normal cognitive developmental stages that lead to acquisition of a theory of mind. In 1985 Baron-Cohen, Leslie and Frith published an article called Does the autistic child have a "theory of mind"? in which it was suggested that the human brain normally has a "theory of mind module" and that this particular component of the brain may not develop normally in some people. With the advent of brain imaging techniques, particular brain regions that seem to be important for theory of mind have been identified. Further autism research by a team at University College London led by Peter Hobson casts light on the crucial stages of infant development.

Autistic people often develop the theory of mind late, or not at all. However, some autistic people claim that the theory of mind that they have developed is superior to that of a normal person. The theory of mind that normal children develop appears to be that other people have different knowledge from themselves, but process their knowledge in the same way that they would.

The usual test for theory of mind - the Sally-Anne test - is biased towards that type of theory of mind. Autistic people who develop a workable theory of mind tend to be aware not only that other people have different knowledge from themselves but also that other people have a different way of thinking. This second aspect of theory of mind is not commonly tested for.

It is not yet established whether this different theory of mind is inherent in the autistic way of thinking or a result of the usual autistic experience of growing up among people with a very radically and obviously different way of thinking. It has also been suggested that the autistic delay in development of theory of mind is to some degree attributable to the difficulty of having to develop this more complex theory.