Thinking
Thinking fills the mind, and in this way defends against the
emptiness of space. Thinking is in fact the inner experience that
corresponds to the ring of tension around the head. Doubt is an
especially efficient form of this defense, because doubt involves
a tightening of the forehead and the eyes, and the centers of
perception in the ocular region. This not only prevents the experience
of space, it also invalidates past experiences of it. (The Void,
pg 91)

Thinking is basically the relating of previously perceived elements
of basic knowledge with each other. The original demarcations
or boundaries that define concepts, words, and images, originate
in basic knowledge. Thinking can then become a dimension on its
own, by the process of relating these mental elements with each
other, in conjunction with further perceptions in present direct
experience, or basic knowledge. This new dimension develops to
many degrees of abstraction; we abstract from the original abstractions,
and create new concepts and symbols that relate to the relationships
of the original abstractions, and to groups of them. This process
develops many degrees of differentiation and integration in an
evolving spiral of self-organization. The original plasticity
of the soul manifests now on this dimension in a much freer way
than we know in direct experience. (Inner Journey Home, pg 59)