« Consciousness does not present itself to itself as broken into fragments. Words such as “chain” or “train” do not describe it as it first gives itself. It is nothing joined together: it flows. A “river” or a “stream” are the metaphors by which it most naturally describes itself. In speaking of it hereafter, let us call it the stream of thought, of consciousness, or of subjective life.

Each thought tends to be part of a personal consciousness.

Within each personal consciousness, thought is always changing.
Within each personal consciousness, thought is sensibly continuous.
It always seems to be concerned with objects independent of itself.
It is interested in certain parts of these objects to the exclusion of others, and it accepts or rejects—in a word, it chooses—throughout its duration.
Consciousness, therefore, does not consist of juxtaposed pieces, but of a flow.
The divisions we draw within it are the result of later réflection.
Nothing is joined; everything flows and transforms itself.
Thought passes and transforms itself without ceasing, and yet it remains itself.
It is not an object; it is a process.»

William James, The Principles of Psychology (1890))

It sometimes happens that a thinker asserts that the mind is not what we believe. Not an inner entity, nor a stable core that would belong to us, but a movement. This assertion is at first unsettling because it removes from the mind any reassuring substance. It leaves only an activity, a process in the act of occurring. What we call “our mind” then ceases to be a place. It becomes a passage.