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Tools Shared, Use Private
A subject takes the tools of language from belonging — the words, the distinctions, the ways of going on are held in common, arriving from the shared side. But the use of those tools, and the understanding built with them, is private: each subject applies what it received slightly differently, from its own position, and ends with a reality that is genuinely its own. The tools are shared; the use is private. That is one fact, not two, and the SPLectrum seed states it whole — P3, that language is where subjects share, and P4, that each source stands equally and unprivileged in what it makes of the shared.
Developmental psychology and the study of language acquisition have circled this fact for a century, and its major figures divide by which end of it they took hold of. Some followed the tools inward, tracing how the common becomes the subject’s own — the convergence direction. Others held onto the privacy of the result, insisting that what each subject builds is irreducibly its own — the divergence direction. And where two minds engage, a third account finds the shared and the private happening at once — the coupling of minds. The same dynamic surfaces at each of these ends and in the meeting between them.
The convergence direction — the common coming in
Vygotsky followed the tools all the way inward. A mental function, on his account, appears twice: first on the social plane, between people, and only afterwards within the person — carried inward by the sign, and by language above all. What the child does in shared activity with others it gradually comes to do alone, and the inner life is the social life taken in. The direction of travel is from the common to the private: the shared tool becomes the subject’s own equipment.
Tomasello supplies the mechanism at the scale of a whole language. Grammar is not switched on from within but built from use — extracted from encountered speech through the reading of others’ intentions and the finding of patterns, assembled piecemeal from concrete instances toward abstract schemas. And the high-fidelity forms of cultural learning are what let a stock of tools accumulate across generations, each cohort inheriting and adding to what the last built — the ratchet that keeps the common stocked. Here the shared is not a backdrop but the very material the subject is made from.
This is the direction the field supplies most readily, and most one-directionally: a crowded, well-attested account of how the common gets into the private. It is the sharing face of the one fact — the tools arriving from belonging, becoming the subject’s own without ceasing to be held in common.
The divergence direction — the result staying private
Kelly held the other end. On his account a person understands the world through a system of personal constructs — bipolar distinctions, built up and tested against experience, through which everything is read. The system is genuinely individual: persons differ in their construction of events, and two people meeting the same situation may construe it in ways that barely overlap. The repertoire is a held thing, the subject’s own, and it is where the privacy of understanding becomes explicit — not a private colouring on a shared picture, but a genuinely individual way of carving the world.
The privacy Kelly names is not a failure of sharing. It is the other direction of the same fact the convergence accounts trace: the tools come from the common, and what each subject makes of them is its own. Where Vygotsky and Tomasello follow the arrow inward, Kelly stands at the far end and describes what the arrow arrives at — a construing that is nobody else’s.
Between the two ends sits Piaget’s constructing subject, which belongs to neither camp and to both: knowledge is neither handed over ready-made nor imprinted from outside, but built by the subject through its own activity — assimilating new experience to what it already holds, and reworking its structures when they fail. The building is the subject’s own work; the material worked on is what belonging supplies. Construction is the hinge on which shared-tools and private-use turn out to be one motion.
Where the directions meet — coupling
Di Paolo, with Hanne De Jaegher, names the place the two directions meet. In participatory sense-making, meaning is generated in the interaction itself — not transmitted from one party to the other, and not drawn ready-made from a shared store, but arising in the coordination between two minds as they engage. The interaction takes on a coherence of its own, and each subject contributes to what arises in it while remaining its own centre.
This is the meeting point because it is where the shared and the private stop being two moments in sequence — the common coming in, then the private going out — and become a single ongoing event. In a real encounter the tools are held in common and deployed from each subject’s own position at once; the shared meaning that neither party held alone is made in the between, out of the private construings both bring. Coupling is the fact seen not from either end but in motion: sharing and privacy as the two things a live exchange is doing in the same moment.
One fact, both ends
Set the four side by side and the question of whether the decisive thing happens inside the person or between people stops looking like a choice. A field that studies the coming-in foregrounds convergence; a field that studies the result foregrounds divergence; a field that studies the live exchange foregrounds coupling. Each has hold of the same thing from where it stands: the tools of language are held in common, and their use is private. The private result is not a deviation from a correct shared version but the ordinary form the shared always takes in a particular subject — which is why the same dynamic reads, without strain, as convergence from one end, divergence from the other, and coupling in the meeting between. Tools shared, use private, seen coming and going.
See also: Human ways of sharing · Sharing Knowledge · Kelly · Vygotsky · Tomasello · Piaget · Di Paolo