Robin Dunbar
The Human Story
A new history of mankind's Evolution
faber and faber 2004
The Art of Mind-reading
At this point, I need to introduce a technical term. Some decades ago, philosophers interested in the nature of minds coined the term 'intentionality' to refer to the kinds of mental states that we have when we are conscious of holding some kind of belief, desire or intention. The term refers collectively to mind-states like knowing, believing, thinking, wanting, desiring, hoping, intending, etc. It refers to the state of being aware of the contents of your own mind. Intentionality can be conceived of as a hierarchically organised series of belief-states.
In this scheme of things, computers are zero-order intentional entities: they are not aware of the contents of their 'minds' Some living organisms such as bacteria (and perhaps some insects) may also be zero-order intentional beings.
Most organisms that have brains of some kind are probably aware of the contents of their minds: they'know' that they are hungry or 'believe' that there is a predator under that bush over there. Such organisms are said to possess first-order intentionality. Having a belief about someone else's beliefs (or intentions) constitutes second order intentionality, the criterion for theory of mind (or, as it is more often known in the technical literature, ToM). Jane believes that Sally thinks her ball is under the cushion. Jane has two belief states in mind (her own and Sally's), so theory of mind is equivalent to second-order intentionality.

Theory of Mind