This inquiry assumes a developmental, eco-cognitive model (Magnani 2017, 2018); it examines how Peirce’s index particularly promotes abductive inferencing (West 2016), initially by individuating pictures and situating events in gestural performatives then by communicating assertions via linguistic performatives (West in press). Index has the unique function of making vivid subjects of discourse, intrapsychologically and interpsychologically (Short 2007); but its influence does not stop there. In facilitating the transition from percept, to “percipuum,” to perceptual judgment, Index establishes the scope of predicates, thereby drawing attention to parameters of objects within events (West 2014, 2018). It is obvious that index is the most efficacious sign to facilitate inferencing in dialogic exchanges because it optimizes eco-cognitive situatedness, maximizes changeability, and because it is particularly sensitive to information pick-up (Magnani 2017: 138). It satisfies these criteria by delimiting shape contours, and by situating their component events in action/state episodes. The ontogeny of proposition-based interpretants begins with object-concept relations, then proceeds to relating events within episodic profiles. Ultimately, index brutely directs interlocutors’ “mental eyeballs” to meanings (1908: 4.350) – those which are ordinarily obscured by patent analogical sign attributes, e.g., resemblance, analogy. The implied nature of index here is essential in “widening” interpretants of “all signs” (1906: 4.538; Bellucci 2014), especially icons. As Seme, index widens meanings of terms, implicating the presence of propositions as commands/interrogatives/suggestions for future conduct, proceeding beyond substitutionary/classificatory functions. As Pheme, index widens propositions via hypotheses of events’ contributory effects; and as Delome explicit arguments promote “double consciousness” (1906: MS 295). In “forcing us to regard” terms as “icons” (1904: EP 2:307), or in suggesting that we do so, index expands the potency of the sign by supplying double consciousness – dialogic exchanges of potential effects. Its greatest expression of double consciousness surfaces when terms/propositions contain imperative/interrogative/subjunctive action-based meanings. (1903: 7.643), where illative force is actualized (1898: MS 485). This is for the Symposium on Cognitive Semiotics.