Intersubjective

Intersubjective, as it appears in Seminar II, names the structural condition in which the subject's reasoning necessarily passes through the thinking of other subjects, constituting a logic that is irreducible to either individual cognition or the mere aggregation of viewpoints. The term is not a sociological descriptor of "relations between persons" but a formal designation: the subject's inference about its own position can only be accomplished by occupying, in thought, the perspective of the other — and crucially, each other subject is doing the same simultaneously. This mutual, reciprocal embedding of perspectives is what generates the three irreducible temporal dimensions Lacan formalizes as Logical Time (the instant of seeing, the time for understanding, the moment to conclude). Intersubjectivity is therefore not a psychological "meeting of minds" but a logical structure in which subjectivity itself is produced through the subject's act of modeling the other modeling it.

The theoretical move of the passage is to ground this intersubjective structure in the three-prisoner puzzle, where no single prisoner has access to sufficient information to determine their own position from a purely private point of view. Resolution is only possible when each subject reasons through what the others must be thinking — and this "must" is a logical necessity, not an empirical guess. What emerges is a topology of reasoning that is constitutively social and temporal: the subject is not a pre-given locus of cognition but is formed in and through the intersubjective circuit. This aligns with the Lacanian principle that the subject is always already constituted by the Other, and that the signifying chain — Language as autonomous system — only becomes Speech (with signification, with subjective intervention) when a subject takes a position within a structure that is shared and reciprocally inhabited.

This concept appears in jacques-lacan-seminar-2 at the juncture where Lacan distinguishes language as an autonomous formal system (the Automaton — the self-running combinatory of signs, independent of any subject) from speech as the act through which a subject introduces Signification. The intersubjective is precisely the hinge: it is the dimension that mathematical formalization (binary code, formal syntax) cannot capture but that the three-prisoner puzzle makes legible. Where Automaton designates repetition without a subject, the intersubjective names the irreducibly temporal and multi-perspectival structure that the subject must inhabit to reach a conclusion — connecting directly to Logical Time's three stages, which are generated by and only by the intersubjective circuit of inference.

The concept also cross-references Language and Signification: Language as a synchronic structure precedes the subject, but it is only through the intersubjective act — each subject reasoning through what the others must think — that Signification (retroactive, quilted meaning) is produced. It touches the Symbolic insofar as the intersubjective structure is governed by the symbolic order's rules, not by Imaginary rivalry or identification: this is not the dyadic mirror-relation of ego to ego (Imaginary) but a triangulated, logical structure of mutual inference. Suture is also implicated, since the subject's "moment to conclude" — the precipitous assertion of certainty — is precisely the sutural act that closes a gap in the signifying chain, stitching the subject into the symbolic at the cost of foreclosing full information. Intersubjective thus sits at the intersection of Logical Time, Language, Symbolic, and Signification, functioning as the concrete logical arena in which all four canonical concepts converge and operate simultaneously.

Seminar II · The Ego in Freud's Theory and in the Technique of PsychoanalysisJacques Lacan · 1954 (p.294)

What's really involved is each of the subject's thinking what the other two must think, and in a completely reciprocal manner.

The phrase "completely reciprocal manner" is theoretically loaded because it names the structural (not merely empirical) symmetry of the intersubjective circuit: each subject's reasoning is not supplementary but constitutive of the others', making the inference irreducibly collective and temporal — precisely the condition that generates Logical Time's three stages and distinguishes subjectivized Speech from the mere automatism of Language as a formal system.