The Continuous Stream
Substantive Perches, Transitive Flights, and the Death of Mental Atoms
No human brain can ever experience the exact same simple sensation twice. That hard physiological boundary stood at the center of William James's January 1884 Mind essay On Some Omissions of Introspective Psychology and the ninth chapter of The Principles of Psychology (1890). For nearly two centuries, the dominant British empiricist school—running from John Locke and David Hume through James Mill, John Stuart Mill, and Alexander Bain—had modeled consciousness as a collection of discrete, repeatable simple ideas. In their account, sensory atoms entered the mind through the eyes and ears. Those mental atoms then hooked together by the laws of association like mosaic tiles laid across a floor.
James demonstrated that mental atomism confuses the static external objects that cause sensations with the living state of the brain that receives them. When a piano key is struck a second time, the acoustic wave in the air is identical to the first. Yet the cerebral cortex it enters has been physically altered by the first sound and by every neural event that occurred in the interval. Experiencing the exact same state of mind twice would require an unmodified brain, which is impossible in a living metabolizing organ. Every perception reflects the global tension of the entire hemisphere at that millisecond. A shaded square on a chessboard looks dark gray in the morning and equally dark gray at noon, yet our subjective feeling of that patch shifts depending on whether our eyes have just looked at a bright window or a black velvet curtain.
Even more damaging to associationist psychology was its blindness to the relational glue of waking thought. Consciousness never appears to itself chopped up in bits. Words like chain or train misdescribe mental life. Only the metaphor of a river or a stream captures how each moment melts continuously into the next. Within that stream, the pace of movement varies constantly. Like a bird's life, consciousness alternates between what James called substantive parts and transitive parts. The substantive parts are stable resting perches occupied by distinct sensory images that can be held before the mind and inspected. The transitive parts are rapid relational flights filled by feelings of direction and tendency that carry the stream from one substantive conclusion to the next.
Why had generations of introspective philosophers missed the transitive flights and insisted that relational words like if, but, by, and although correspond to nothing in the mind? The sole biological function of a transitive flight is to propel thought from one substantive perch to another. The moment an introspectionist stops a transitive flight in mid-air to examine it as a static picture, he destroys the movement itself. In The Principles of Psychology, James observed that trying to inspect a transitive flight by freezing it in place is like trying to turn up a gas lamp quickly enough to see how the darkness looks.
Every substantive perch is also surrounded by a psychic overtone, halo, or fringe of faintly waxing and waning cortical excitations. When we try to recall a forgotten name, consciousness is not an empty gap. It is an active, tuned filter that immediately rejects any wrong syllable because the surrounding neural halo is already pre-activating the semantic neighborhood of the missing word before the word itself reaches the tongue.
Two years after reading James's chapter on the stream of thought in London, novelist May Sinclair borrowed the phrase in a 1918 review of Dorothy Richardson's fiction, turning a Harvard neurophysiological critique into the defining technique of twentieth-century modernist literature.