By Matt Harrington, BCBA · Behaviorist Book Club · April 2026 · 12 min read

Emergent Relations and Stimulus Equivalence: Theory and Clinical Applications in ABA

Overview & Clinical Significance

The question of whether emergent relations are truly emergent — whether they arise from processes fundamentally different from directly trained stimulus-response associations — sits at the intersection of basic behavioral science and clinical application in a way that has substantial practical consequences. For BCBAs, understanding stimulus equivalence, derived relational responding, and the theoretical accounts offered for these phenomena informs decisions about verbal behavior programming, language intervention, and the design of instructional procedures for clients with diverse learning histories.

Hank Schlinger and Eb Blakely bring complementary expertise to this discussion. Schlinger's background in radical behaviorism, child development, and scientific psychology positions him to evaluate emergent relations within the broader framework of a rigorous behavior analytic epistemology. Blakely's work in radical behaviorism and behavior pharmacology brings attention to the physiological and theoretical underpinnings of behavioral phenomena. Their conversation explores whether the term emergent adequately captures what is happening when an organism demonstrates stimulus relations it was never directly trained to produce — and whether alternative accounts explain the data more parsimoniously.

This question matters clinically because stimulus equivalence training has become a standard component of comprehensive verbal behavior programs. Understanding what the research actually demonstrates — and what remains theoretically contested — helps BCBAs implement these procedures with appropriate confidence and appropriate humility. Practitioners who understand the debate between mediational and other accounts of stimulus equivalence are better positioned to design procedures that are experimentally sound and clinically defensible.

Background & Context

Stimulus equivalence research has a substantial empirical history in behavior analysis. The foundational work established that after training A→B and A→C relations, organisms often demonstrate derived relations including symmetry (B→A, C→A), transitivity (B→C, C→B), and combined symmetry-transitivity (C→B, B→C) — the defining properties of an equivalence class. These derived relations emerge without direct training, which has led to substantial theoretical interest in explaining the mechanism by which they appear.

Murray Sidman's formulation of stimulus equivalence remains influential, treating equivalence as a basic behavioral phenomenon not reducible to other behavioral processes. The derived relational responding account, associated with Relational Frame Theory (RFT), offers an alternative explanation: that responding in accordance with derived stimulus relations is a class of operant behavior that is itself learned, with arbitrarily applicable relational responding as the critical behavioral unit. A mediational account, referenced in the course description, proposes that common mediating responses — either overt or covert — account for derived relations without requiring the concept of emergence.

The clinical significance of this theoretical debate is not merely academic. How BCBAs conceptualize the mechanism of language acquisition and verbal behavior shapes the design of instructional programs. If derived relational responding is itself trainable behavior, then directly targeting the learning-to-learn processes underlying language — as RFT-based interventions propose — has clinical implications distinct from those following from accounts that treat equivalence as automatically emergent from specific training histories.

Schlinger's work on a mediational account of verbal behavior is situated within a broader commitment to parsimony in behavioral science — preferring explanations grounded in established behavioral processes over those requiring new theoretical constructs. This methodological commitment has practical implications for how BCBAs evaluate the rapidly expanding literature on derived relational responding and its clinical applications.

Clinical Implications

The most direct clinical implication of understanding emergent relations is for the design of verbal behavior programs. Teaching a child to match a spoken word to an object (A→B) and to select an object given a picture (A→C) may result in the emergence of the picture-word relation (B→C) without direct training — but only under certain conditions. BCBAs who understand these conditions — including the role of the training structure, the history of the organism, and the similarity of the stimuli involved — can design programs that maximize the probability of derived relation formation and measure it appropriately.

For clients with severe language delays or those who have demonstrated limited derived relational responding historically, the theoretical accounts discussed in this course have different practical implications. If emergent relations are automatically produced by specific training histories, then ensuring the training structure is adequate should be sufficient. If derived relational responding is itself a learned behavior requiring direct training, then clients who fail to demonstrate equivalence may need explicit training in the relational frames underlying it rather than simply more exposure to the original training history.

Verbal behavior programming is also implicated through the tact-mand distinction and the role of stimulus control in each. Understanding how arbitrary symbolic relations are established — the process by which a spoken sound comes to control behavior in the same way as the referent it names — has direct implications for how BCBAs sequence language instruction. The debate about whether this process is emergent or mediated affects clinical decisions about when to probe for derived relations, what to do when they fail to emerge, and how to interpret variability in equivalence class formation across clients.

Assessment of verbal behavior is enhanced by practitioner familiarity with stimulus equivalence research. Tools like the VBMAPP include items targeting conditional discrimination, which is foundational to equivalence formation. BCBAs who understand the experimental parameters of equivalence research — the matching-to-sample procedure, the importance of baseline training structure, the distinction between symmetry and transitivity — interpret assessment data with greater precision.

Ethical Considerations

The ethical dimensions of this course are primarily those associated with the application of theoretical knowledge to clinical practice — specifically, the obligation to represent the state of knowledge accurately and to implement procedures with appropriate justification. Code 2.01 requires behavior analysts to provide services within defined areas of competence, and theoretical understanding of verbal behavior and stimulus equivalence is part of the competence required for designing comprehensive language programs.

Code 6.01 requires use of scientifically supported procedures, which in the context of emerging or debated theoretical frameworks requires careful judgment. The experimental literature on stimulus equivalence is substantial and replicable; the debate is about mechanism, not about whether the phenomena are real. BCBAs can implement equivalence-based programming with confidence in the empirical phenomena while maintaining theoretical humility about which explanatory account is most accurate.

Code 1.04's integrity requirement applies to how BCBAs represent the evidence base to families and interdisciplinary team members. When discussing verbal behavior programming with parents or other professionals, BCBAs should accurately represent what equivalence training accomplishes, what evidence supports its use, and what remains theoretically contested — without either overstating certainty or understating the robustness of the empirical findings.

The intellectual engagement modeled by Schlinger and Blakely — rigorous evaluation of theoretical accounts, willingness to consider alternative explanations, commitment to parsimony — reflects the scientist-practitioner standard that Code 1.04 and the broader BACB competency framework require. BCBAs who engage with theoretical debates in their field demonstrate the kind of continuous professional development that ethical practice demands.

Assessment & Decision-Making

Assessing whether a client demonstrates stimulus equivalence requires systematic probing using match-to-sample procedures with controlled training histories. BCBAs should establish trained conditional discriminations (A→B, A→C) using a structure that has been shown to produce equivalence in the research literature, then probe for derived relations (B→C, C→B, symmetry relations) with novel probe trials that have not received direct reinforcement. Documenting baseline accuracy on probe trials before training begins establishes whether the derived relations emerge from the training history rather than from prior learning.

When a client fails to demonstrate derived relations following appropriate training, BCBAs face a decision point about how to proceed. One option is to extend the training history, adding more trained relations. Another is to directly train the failing relations. A third — consistent with the theoretical accounts discussed in this course — is to examine whether the client has the prerequisite conditional discrimination skills and relational learning history required for equivalence formation. This decision requires familiarity with the experimental literature on factors that affect equivalence class formation.

For verbal behavior program design, decision-making about which stimulus relations to train is informed by understanding the client's current verbal operant repertoire, the relations that have functional significance in the natural environment, and the theoretical literature on which training structures produce the most reliable equivalence class formation. The sequence of training — whether to use a linear series (A→B, B→C) or a sample-as-node structure (A→B, A→C) — affects the probability of derived relation formation and should be chosen deliberately.

Interpretation of probe data requires attention to potential sources of false positives (such as generalized matching responses) and false negatives (such as insufficient baseline training, procedural confounds, or motivational factors). BCBAs should design probes with sufficient intertrial intervals, control for response position biases, and collect data across multiple sessions before drawing conclusions about equivalence class formation.

What This Means for Your Practice

Engaging with the theoretical debate about whether emergent relations are truly emergent is not an abstract exercise — it directly shapes how BCBAs design and implement verbal behavior programs for clients with language delays and how they interpret the outcome data these programs generate.

For practitioners who currently implement equivalence-based programming, this course should prompt a review of the training structures being used and whether they are consistent with the experimental literature on conditions that produce reliable derived relation formation. Are baseline trained relations achieving sufficient accuracy before probing? Are probes designed to exclude previous reinforcement history? Are equivalence class outcomes being tracked with sufficient precision to inform programming decisions?

For practitioners less familiar with equivalence-based approaches, this course provides an entry point into a literature that has substantial clinical applicability for language programming. The matching-to-sample procedure is accessible and amenable to implementation in standard ABA settings. Starting with simple two-class equivalence programs and systematically evaluating derived relation formation provides a low-barrier way to integrate this evidence base into verbal behavior practice.

At a broader level, engaging with theoretical debates in behavior analysis — staying current with competing accounts of behavioral phenomena, evaluating evidence rather than defaulting to familiar frameworks — is part of what the scientist-practitioner identity requires. Schlinger and Blakely's discussion models intellectual engagement that is its own form of professional development: examining the conceptual foundations of what we do, asking whether our explanations are as parsimonious as they could be, and remaining open to better accounts as the evidence develops.