Our ability to understand this concept is based on our sharing a number of key aspects of the phrase that are normally only implicit and unconsciously evoked. Consider the parallel construction, “a cup can be out of its cupboard.” This is a literal concrete case that illustrates the logical relationships involved in both concepts.
We know, by the use of ‘its’, that cups belong in cupboards, which are bounded regions in space.
We implicitly know that cupboards are a feature of rooms, which are also bounded regions in space, therefore we know by logical inference that cups belong in rooms.
We know that in this instance we are considering the cup as a location even though it, too, is a bounded region in space.
We know that the cup-as-location has the possibility of being in specified relations to (out and, by logical inference, in) the cupboard though in only partially specified relations to the room (we do not know from this phrase if the cup can be out of the room though experientially we know it can.)
Returning to what we know about “a man can be out of his mind”-
Minds are what cause the behavior of creatures.
A man is the kind of creature that has a mind which is an important aspect of his whole self.
A mind can be understood as a bounded region in space, presumably within the space that constitutes a whole self. Thus, a mind is logically equivalent to the cupboard and a whole self is logically equivalent to the room in which the cupboard is located.
A man’s true self is another distinct part of the whole self and the true self can be understood as a location that has some relationship to the bounded region of mind. Thus, the true self is logically equivalent to the cup that is supposed to be in the mind which is located within the whole self.
While a mind is only one aspect of self, it is distinct from a true self which is the locus of will and a person’s will must be present as one behaves to be held responsible for the consequences of those actions. We make exceptions to important rules for social behavior based on this normative conception of what it takes to be held responsible for our actions.
Under some circumstances the true self is not the cause of a man’s behavior.
When the true self is located outside of the bounded region that causes his behavior then we can say, ”he is out of his mind” which implies that he is not behaving normally and is not strictly responsible for what occurs as a result of those particular behaviors.
Note that a mind does not literally occupy space. We cannot literally perceive minds in any concrete way. Minds are a concept we use to think about the causes of people’s behaviors, this is the literal core meaning of the concept of a 'mind.' Since we also conceive of a person's behavior as classified into separate groups, normal behaviors and abnormal behaviors, then we use the metaphor of boundaries within the space of mind to understand different type of behavior. There is a literal core, but the ways we think and reason about minds are mostly metaphorical. A man can be out of his mind because of the ways we understand the logic of literal spatial relations as applied to the idea that a mind is the cause of behaviors.